Catalysts

Monday June 19, 2017

Chemists want to control not only what comes out of a chemical reaction, but how fast the reaction occurs. For example, scientists are working to slow down the depletion rate of the ozone in the upper level of our atmosphere, so we stay protected from harmful UV rays.


The rate of the chemical reaction of a nail rusting is slow compared to how fast baking soda reacts with vinegar. Different factors affect the speed of the reaction, but the main idea is that the more collisions between particles, the faster the reaction will take place.
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A catalyst can also slow down a reaction. A catalytic promoter increases the activity, and a catalytic poison (also known as a negative catalyst, or inhibitor) decreases the activity of a reaction.


Catalysts offer a different way for the reactants to become products, and sometimes this means the catalyst reacts during the chemical reaction to form intermediates. Since the catalyst is completely regenerated before the reaction is finished, it’s considered ‘not used’ in the overall reaction.


A catalytic converter, like the one you’ll find on cars, takes harmful molecules that come out of the engine like hydrocarbons, carbon monoxide, and nitrogen oxide and converts it into harmless molecules that don’t hurt the environment. The catalyst in these is usually platinum and palladium and it converts carbon monoxide to carbon dioxide, hydrocarbons into carbon dioxide and water, and nitrogen oxide into nitrogen and oxygen, stuff we use to breathe in our atmosphere. The picture of the one in the upper left is from a diesel engine, and the image in the lower right is the kind you’ll find under your car connected to the tailpipe.


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Hydrolysis

Monday June 19, 2017

This experiment is for advanced students. Hydrolysis is a chemical reaction that involves breaking a molecular bond using water. In chemistry, there are three different types of hydrolysis: sat hydrolysis, acid hydrolysis, and base hydrolysis. In nature, living organisms survive by making their energy from processing food. The energy converted from food is stored in ATP molecules. To release the energy stored in food, a phosphate group breaks off an ATP molecule (and becomes ADP) using hydrolysis and releases energy from the bonds.


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Materials:


  • raw egg
  • copper sulfate
  • sodium hydroxide
  • 3 test tubes with stoppers
  • distilled water
  • safety goggles and gloves


Put simply, hydrolysis is a chemical reaction that happens when a molecule splits into two parts when water is added. One part gains a hydrogen (H+) and the other gets the hydroxyl (OH–) group. The reaction in the experiment forms starch from glucose, and when we add water, it breaks down the amino acid components just like the enzymes do in your stomach when they digest food.


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Rates of reactions

Monday June 19, 2017

Hydrolysis is a chemical reaction that happens when a molecule splits into two parts when water is added. One part gains a hydrogen (H+) and the other gets the hydroxyl (OH–) group. The reaction in the experiment forms starch from glucose, and when we add water, it breaks down the amino acid components just like the enzymes do in your stomach when they digest food.


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Other states of matter

Monday June 19, 2017

Plasma makes up a very large percentage of the matter in the universe. Not much of it is on Earth and the plasma that is here is very short lived or stuck in a tube. Plasma is basically what happens when you add enough energy to a gas that the atoms move and vibrate around so energetically that they smack into each other and rip electrons off each other, so you have positively charged atoms (called ions) that lost their electrons, and also the electrons themselves which are negatively charged, all zinging around in the gas.
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This gives the gas electrical properties that gases don’t usually have, so it’s classified as a different state of matter, or known as “ionized gas” – it’s gas that is electrically charged. The stuff in florescent light bulbs is plasma. Plasma TV’s have plasma inside of them. Lightning and sparks are actually plasma!


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Click here for the next lesson in Osmosis.

Desalination

Monday June 19, 2017

This experiment is for advanced students.Have you ever taken a gulp of the ocean? Seawater can be extremely salty! There are large quantities of salt dissolved into the water as it rolled across the land and into the sea. Drinking ocean water will actually make you thirstier (think of eating a lot of pretzels). So what can you do if you’re deserted on an island with only your chemistry set?


Let me show you how to take the salt out of water with this easy setup.


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Materials:


  • salt
  • water
  • alcohol burner
  • flask with one-hole stopper
  • stand with wire mesh screen
  • two 90-degree glass pipes
  • flexible tubing
  • ring stand with clamp
  • lighter with adult help


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PVA

Monday June 19, 2017

Instead of using glue as a polymer (as in the slime recipes above), we're going to use PVA (polyvinyl alcohol). Most liquids are unconnected molecules bouncing around. Monomers (single molecules) flow very easily and don't clump together. When you link up monomers into longer segments, you form polymers (long chains of molecules).

Polymers don't flow very easily at all - they tend to get tangled up until you add the cross-linking agent, which buddies up the different segments of the molecule chains together into a climbing-rope design.

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Materials:

Here's what you do:


Download Student Worksheet & Exercises

By adding borax to the mix, you cross-link the long chains of molecules together into a fishnet, and the result is a gel we call slime. PVA is used make sponges, hoses, printing inks, and plastic bags.

You can add food coloring (or a bit of liquid Ivory dish soap to get a marbled appearance). You can also add a dollop of titanium dioxide sunscreen to your slime before cross-linking it to get a metallic sheen.

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Glowing Slime

Monday June 19, 2017

When you think of slime, do you imagine slugs, snails, and puppy kisses? Or does the science fiction film The Blob come to mind? Any way you picture it, slime is definitely slippery, slithery, and just plain icky — and a perfect forum for learning real science.


But which ingredients work in making a truly slimy concoction, and why do they work? Let’s take a closer look…


Imagine a plate of spaghetti. The noodles slide around and don’t clump together, just like the long chains of molecules (called polymers) that make up slime. They slide around without getting tangled up. The pasta by itself (fresh from the boiling water) doesn’t hold together until you put the sauce on. Slime works the same way. Long, spaghetti-like chains of molecules don’t clump together until you add the sauce … until you add something to cross-link the molecule strands together.


The sodium-tetraborate-and-water mixture is the “spaghetti” (the long chain of molecules, also known as a polymer), and the “sauce” is the glue-water mixture (the cross-linking agent). You need both in order to create a slime worthy of Hollywood filmmakers.


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Materials:


  • popsicle sticks
  • water
  • disposable cups
  • borax (laundry whitener)
  • clear glue (or glue gel) or white glue
  • yellow highlighter
  • measuring spoons
  • scissors
  • UV black light


 
Download Student Worksheet & Exercises


To make this slime, combine ½ cup of water with 1 teaspoon of sodium tetraborate (also known as ‘Borax’) in a cup and stir with a popsicle stick.


In another cup, mix equal parts white glue and water. Add a glob of the glue mixture to the sodium tetraborate mixture. Stir for a second with a popsicle stick, then quickly pull the putty out of the cup and play with it until it dries enough to bounce on the table (3 to 5 minutes). Pick up an imprint from a textured surface or print from a newspaper, bounce and watch it stick, snap it apart quickly and ooze it apart slowly …


To make glowing slime, add one simple ingredient to make your slime glow under a UV light (or in sunlight)! You’ll need to extract the dye from the felt of a bright yellow highlighter pen and use the extract instead of water. (Simply cut open the pen and let water trickle over the felt into a cup: instant glow juice.) For the best slime results, substitute clear glue or glue gel for the white glue.


Don’t forget: You’ll need a long-wave UV source (also known as a “black light”) to make it glow (fluorescent lights tend to work better than incandescent bulbs or LEDs) – check the shopping list for where to get one. This slime will glow faintly in sunlight, because you get long-wave UV light from the sun — it’s just that you get all the other colors, too, making it hard to see the glow.


Is your slime a solid, a liquid, or a bubbly gas? The best slimes we’ve seen have all three states of matter simultaneously: solid chunks suspended in a liquidy form with gas bubbles trapped inside. Yeecccccch!!


What other stuff glows under a black light? Loads of stuff! There are a lot of everyday things that fluoresce (glow) when placed under a black light. Note that a black light emits high-energy UV light. You can’t see this part of the spectrum (just as you can’t see infrared light, found in the beam emitted from the remote control to the TV), which is why “black lights” were named that. Stuff glows because fluorescent objects absorb the UV light and then spit light back out almost instantaneously. Some of the energy gets lost during that process, which changes the wavelength of the light, which makes this light visible and causes the material to appear to glow. (More on this in Unit 9.)


How to Make Glow Juice

You can add glow juice in place of water in any experiment. Here’s how you make the glow juice by itself:



Moon Blob

moonblobThe most slippery substance on the planet, this dehydrated gel is a super-slippery, super long polymer chain of molecules that will actually climb up and out of your container if you don’t use a lid.  This slime is sensitive to light, temperature, and concentration (the amount of water you use) so if yours isn’t very responsive, check those three things.


Mixing this gel takes at least two days, and when you do it, make only a half recipe so you can make adjustments if yours isn’t quite right. We use ours on ‘Slip and Slides’ instead of water for a super-fun ride! (Hint – don’t try to stand, or you’ll break your arm when you crash!)


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Bouncy Putty

Monday June 19, 2017

The glue is a polymer, which is a long chain of molecules all hooked together like tangled noodles. When you mix the two solutions together, the water molecules start linking up the noodles together all along the length of each noodle to get more like a fishnet. Scientists call this a polymetric compound of sodium tetraborate and lactated glue. We call it bouncy putty.


Here’s what you do:


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  1. Combine ½ cup water with one teaspoon of Borax in a cup and stir with a popsicle stick.
  2. In another cup, mix equal parts white glue and water.
  3. Add in a glob of glue mixture to the borax.
  4. Stir for one second with a popsicle stick, then quickly pull the putty out of cup and play with it until it dries enough to bounce on table (3-5 minutes).
  5. Pick up an imprint from a textured surface or print from a newspaper, bounce and watch it stick, snap it apart quickly and ooze apart slowly.


Download Student Worksheet & Exercises
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Bouncy Ball

Monday June 19, 2017

This is one of those ‘chemistry magic show’ type of experiments to wow your friends and family. Here’s the scoop: you take a cup of clear liquid, add it to another cup of clear liquid, stir for ten seconds, and you’ll see a color change, a state change from liquid to solid, and you can pull a rubber-like bouncy ball right out of the cup.


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If you have trouble locating the ingredients, you can order them online here:


  • Sodium Silicate (from Unit 3) MSDS
  • Ethyl Alcohol (check your pharmacy) MSDS
  • Disposable cups (at least two – and don’t use your kitchen glassware, as you’ll never get it clean again)
  • Popsicle sticks (again, use something disposable to stir with)


Download Student Worksheet & Exercises


1. In one cup, measure four tablespoons of sodium silicate solution (it should be a liquid). Sodium silicate can be irritating to the skin for some people, so wear rubber gloves when doing this experiment!


2. Measure 1 tablespoon of ethyl alcohol into a second cup. Ethyl alcohol is extremely flammable—cap it and keep out of reach when not in use.


3. Pour the alcohol into the sodium silicate solution and stir with a Popsicle stick.


4. You’ll see a color change (clear to milky-white) and a state change (liquid to a solid clump.


5. Using gloves, gather up the polymer ball and firmly squeeze it in your hands.


6. Compress it into the shape you want—is it a sphere, or do you prefer a dodecahedron?


7. Bounce it!


8. Be patient when squeezing the compound together. If it breaks apart and crumbles, gather up the pieces and firmly press together.


Store your bouncy ball in a Ziploc bag!


What’s Going On?

Silicones are water repellent, so you’ll find that food dye doesn’t color your bouncy ball. You’ll find silicone in greases, oils, hydraulic fluids, and electrical insulators.


The sodium silicate is a long polymer chain of alternating silicon and oxygen atoms. When ethanol (ethyl alcohol) is added, it bridges and connects the polymer chains together by cross-linking them.


Think of a rope ladder—the wooden rungs are the cross-linking agents (the ethanol) and the two ropes are the polymer chains (sodium silicate).


Safety information for Sodium Silicate: MSDS.


Questions to Ask


1. Before the reaction, what was the sodium silicate like? Was it a solid, liquid, or gas? What color was it? Was it slippery, grainy, viscous, etc.?


2. What was the ethanol like before the reaction?


3. How is the product (the bouncy ball) different from the two chemicals in the beginning?


4. Was the bouncy ball  the only molecule that was formed?


5.  Was this reaction a physical or chemical change?


Did you know? Silly putty is actually a mixture of silicone and chalk!


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Colloids and Polymers

Monday June 19, 2017

Imagine a plate of spaghetti. The noodles slide around and don’t clump together, just like the long chains of molecules (called polymers) that make up slime. They slide around without getting tangled up. The pasta by itself (fresh from the boiling water) doesn’t hold together until you put the sauce on. Slime works the same way. Long, spaghetti-like chains of molecules (called polymers) don’t clump together until you add the sauce – something that cross-links the molecule strands (polymer) together.
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Scientists call this a non-Newtonian fluid. You can also fill an empty water bottle or a plastic test tube half-full with this stuff and cap it. Notice that when you shake it hard, the slime turns into a solid and doesn’t slosh around the tube. When you rotate the tube slowly, it acts like a liquid.


About 80% of the organic chemistry industry is devoted to making synthetic polymers. If you’re planning to become a chemical engineer, your chances of working with polymers is pretty high! You find polymers everywhere – plastic bottles are made of polyethylene, frying pans coated with teflon, clothes made from polyester, shoes from synthetic materials. There are two main categories of polymers – natural and synthetic. The ones I just mentioned are synthetic, like PVC and polystyrene foam. Natural polymers include DNA and cellulose.


A colloid is a mixture where one substance is suspended throughout another. When we make slime, the borax is the colloid and the borax-water solution is the colloidal suspension (borax will somewhat settle out after a bit of time, but some of it still remains dispersed in the water.) When you add a polymer (the glue), it forms a gel network and you get slime!


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Supercooling

Thursday June 15, 2017

Did you know that supercooled liquids need to heat up in order to freeze into a solid? It’s totally backwards, I know…but it’s true! Here’s the deal:


A supercooled liquid is a liquid that you slowly and carefully bring down the temperature below the normal freezing point and still have it be a liquid. We did this in our Instant Ice experiment.


Since the temperature is now below the freezing point, if you disturb the solution, it will need to heat up in order to go back up to the freezing point in order to turn into a solid.


When this happens, the solution gives off heat as it freezes. So instead of cold ice, you have hot ice. Weird, isn’t it?


Sodium acetate is a colorless salt used making rubber, dying clothing, and neutralizing sulfuric acid (the acid found in car batteries) spills. It’s also commonly available in heating packs, since the liquid-solid process is completely reversible – you can melt the solid back into a liquid and do this experiment over and over again!


The crystals melt at 136oF (58oC), so you can pop this in a saucepan of boiling water (wrap it in a towel first so you don’t melt the bag) for about 10 minutes to liquify the crystals.


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Materials:


  • Sodium Acetate
  • Disposable aluminum pie plate


Download Student Worksheet & Exercises


You have seen this stuff before – when you combined baking soda and vinegar in a cup, the white stuff at the bottom of the cup left over from the reaction is sodium acetate. (No white stuff? Then it’s mixed in solution with the water. If you heat the solution and boil off all the water, you’ll find white crystals in the bottom of your pan.) The bubbles released from the baking soda-vinegar reaction are carbon dioxide.


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Triple Point

Thursday June 15, 2017

Find a low pressure (like the pressure you feel right now – it’s called 1 atm). Put your finder on the 1 mark on the vertical side (next to the “P”, which stands for Pressure) and follow the dashed line straight across. As you move across, so you notice how at low temperatures you’re in the ice region, but when you hit zero, you turn to water, and for temperatures below 100 deg C you’re only in the liquid water phase?


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The triple point is where a molecule can be in all three states of matter at the exact same time, all in equilibrium. Imagine having a glass of liquid water happily together with both ice cubes and steam bubbles inside, forever! The ice would never melt, the liquid water would remain the same temperature, and the steam would bubble up but not melt the ice. In order to do this, you have to get the pressure and temperature just right, and it’s different for every molecule.


The triple point of mercury happens at -38oF and 0.000000029 psi. For carbon dioxide, it’s 75psi and -70oF. So this isn’t something you can do with a modified bike pump and a refrigerator.


However, the triple point of water is 32oF and 0.089psi. The only place we’ve found this happening naturally (without any lab equipment) is on the surface of Mars.


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Genie in a Bottle

Thursday June 15, 2017

While this isn’t actually an air-pressure experiment but more of an activity in density, really, it’s still a great visual demonstration of why Hot Air Balloons rise on cold mornings.


Imagine a glass of hot water and a glass of cold water sitting on a table, side by side. Now imagine you have a way to count the number of water molecules in each glass. Which glass has more water molecules?


The glass of cold water has way more molecules… but why? The cold water is more dense than the hot water. Warmer stuff tends to rise because it’s less dense than colder stuff and that’s why the hot air balloon in experiment 1.10 floated up to the sky.


Clouds form as warm air carrying moisture rises within cooler air. As the warm, wet air rises, it cools and begins to condense, releasing energy that keeps the air warmer than its surroundings. Therefore, it continues to rise. Sometimes, in places like Florida, this process continues long enough for thunderclouds to form. Let’s do an experiment to better visualize this idea.


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Materials: Two identical tall glasses, hot water, cold water, red and blue food dye, and an index card larger enough to cover the opening of the glasses



Fill two identical water glasses to the brim: one with hot water, the other with cold water. Put a few drops of blue dye in the cold water, a few drops of red dye in the hot water. Place the index card over the mouth of the cold water and invert the glass over the glass of hot water. Line up the openings of both glasses, and slowly remove the card.


Troubleshooting: Always invert the cold glass over the hot glass using an index card to hold the cold water in until you’ve aligned both glasses. You can also substitute soda bottles for water glasses and slide a washer between the two bottles to decrease the flow rate between the bottles so the effect lasts longer.


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Freeze Swap

Thursday June 15, 2017

Indoor Rain Clouds

Making indoor rain clouds demonstrates the idea of temperature, the measure of how hot or cold something is. Here’s how to do it:


Take two clear glasses that fit snugly together when stacked. (Cylindrical glasses with straight sides work well.)


Fill one glass half-full with ice water and the other half-full with very hot water (definitely an adult job – and take care not to shatter the glass with the hot water!). Be sure to leave enough air space for the clouds to form in the hot glass.


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Place the cold glass directly on top of the hot glass and wait several minutes. If the seal holds between the glasses, a rain cloud will form just below the bottom of the cold glass, and it actually rains inside the glass! (You can use a damp towel around the rim to help make a better seal if needed.)


Materials:


  • glass of ice water
  • glass of hot water (see video)
  • towel
  • adult help


  Download Student Worksheet & Exercises


Bottling Clouds

On a stormy, rainy afternoon, try bottling clouds — using the refrigerator! Here’s what you do: Place an empty, clean 2-liter soda bottle in the fridge overnight. Take it out and get an adult to light a match, letting it burn for a few seconds, then drop it into the bottle. Immediately cap the bottle and watch what happens (you should see smoke first, then clouds forming inside). Squeeze the sides of the bottle. The clouds should disappear. When you release the bottle, the clouds should reappear. Materials:


  • 2L soda bottle
  • rubbing alcohol
  • bicycle pump
  • car tire valve (drill a 1/2 inch hole through a 2L soda bottle cap and pull the valve gently through with pliers)


Advanced Idea: You can substitute rubbing alcohol and a bicycle pump for the matches to make a more solid-looking cloud.  Swirl a bit of rubbing alcohol around inside the bottle, just enough to coat the insides, and then pour it out.  Cap your bottle with a rubber stopper fitted with a needle valve (so the valve is poking out of the bottle), and apply your pump.  Increase the pressure inside the bottle (keep a firm hand on the stopper or you’ll wind up firing it at someone) with a few strokes and pull out the stopper quickly.  You should see a cloud form inside.


What’s going on? Invisible water vapor is all around us, all the time, but they normally don’t stick together. When you squeezed the sides of the bottle, you increased the pressure and squeezed the molecules  together.  Releasing the bottle decreases the pressure, which causes the temperature to drop. When it cools inside, the water molecules stick to the smoke molecules, making a visible cloud inside your bottle.


Did you know that most drops of water actually form around a dust particle?  Up in the sky, clouds come together when water vapor condenses into liquid water drops or ice crystals. The clouds form when warm air rises and the pressure is reduced (as you go up in altitude). The clouds form at the spot where the temperature drops below the dew point.


The alcohol works better than the water because it evaporates faster than water does, which means it moves from liquid to vapor more easily (and vividly) than regular old water.


Questions to ask:


  • How many times can you repeat this?
  • Does it matter what size the bottle is?
  • What if you don’t chill the bottle?
  • What if you freeze the bottle instead?

Exercises


  1. Which combination made it rain the best? Why did this work?
  2. Draw your experimental diagram, labeling the different components:
  3. Add in labels for the different phases of matter. Can you identify all three states of matter in your experiment?

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Phase changes and temperature

Thursday June 15, 2017

When something changes state, goes from like a liquid to a solid, all of the substance must change to the next state. For example, at 100° C all the water must change from a liquid to a gas. The temperature stays constant until it’s completely changed state. It’s kind of weird when you think about it.


If you were able to take the temperature of water as it changed from a solid (ice) to a liquid you would notice that the temperature stays at 32° F until that piece of ice was completely melted. The temperature would not increase at all.


Even if that ice was in an oven, the temperature would stay the same. Once all the solid ice had disappeared, then you would see the temperature of the puddle of water increase.
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Liquid Nitrogen

Thursday June 15, 2017

As promised, here’s the Liquid Nitrogen Ice Cream Social video that was only available to a handful of participants at our live summer camp last week! This is probably one of the last times Dr. Tom Frey will be doing this presentation, so we didn’t want to miss the opportunity to record it and share it with you!


Dr. Tom Frey just retired as a chemistry professor at Cal Poly State University, where he taught courses (including how to make your own lab glassware) for 42 years. He’s not only a mentor of mine, but a close personal friend and I am happy to share his talent and passion for science with you through this special, one of a kind video.


I really hope you enjoy it!


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Let me know what you think!


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Liquids

Thursday June 15, 2017

A liquid has a definite volume (meaning that you can’t compress or squish it into a smaller space), but takes the shape of its container. Think of a water-filled balloon. When you smoosh one end, the other pops out. Liquids are generally incompressible, which is what hydraulic power on heavy duty machinery (like excavators and backhoes) is all about.


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Borax Crystals

Thursday June 15, 2017

Can we really make crystals out of soap?  You bet!  These crystals grow really fast, provided your solution is properly saturated.  In only 12 hours, you should have sizable crystals sprouting up.


You can do this experiment with either skewers, string, or pipe cleaners.  The advantage of using pipe cleaners is that you can twist the pipe cleaners together into interesting shapes, such as a snowflake or other design.  (Make sure the shape fits inside your jar. )


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Here’s what you need:


  • pipe cleaners (or string or skewer)
  • cleaned out pickle, jam, or mayo jar
  • water
  • borax (AKA sodium tetraborate)
  • adult help, stove, pan, and stirring spoon

Here’s what you do:


1. Cut a length of string and tie it to your pipe cleaner shape; tie the other end around a pencil or wooden skewer. You want the shape suspended in the jar, not touching the bottom or sides.


2. Bring enough water to fill the jar (at least 2 cups) to a boil on the stove (food coloring is fun, but entirely optional).


3. Add 1 cup of borax (aka sodium tetraborate or sodium borate) to the solution, stirring to dissolve. If there are no bits settling to the bottom, add another spoonful and stir until you cannot dissolve any more borax into the solution. When you see bits of borax at the bottom, you’re ready.  (You’ll be adding in a lot of borax, which is why we asked you to get a full box). You have made a supersaturated solution.  Make sure your solution is saturated, or your crystals will not grow.


4. Wait until your solution has cooled to about 130oF (hot to the touch, but not so hot that you yank your hand away). Pour this solution (just the liquid, not the solid bits) into the jar with the shape.  Put the jar in a place where the crystals can grow undisturbed overnight, or even for a few days.  Warmer locations (such as upstairs or on top shelves) is best.



 
Download worksheet and exercises


DO  NOT EAT!!! Keep these crystals out of reach of small kids, as they look a lot like the Rock Candy Crystals.


Here are photos from kids ages 2, 7, 9 that made their own! Great job to the Fluker Family!!


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Solids

Thursday June 15, 2017

Solids
What makes the solids, liquids, gases etc. different is basically the energy (motion) of the atoms. From BEC, where they are so low energy that they are literally blending into one another, to plasma, where they are so high energy they can emit light. Solids are the lowest energy form of matter that exist in nature (BEC only happens under laboratory conditions).


In solids, the atoms and molecules are bonded (stuck) together in such a way that they can’t move easily. They hold their shape. That’s why you can sit in a chair. The solid molecules hold their shape and so they hold you up. The typical characteristics that solids tend to have are they keep their shape unless they are broken and that they do not flow.


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Elasticity is what allows you to bounce a basketball and shoot a rubber band across the room. All solids have some elasticity. A rubber band has a lot of elasticity, a diamond on the other hand has very little elasticity. Elasticity is basically the ability of solids to be stretched, twisted or squashed and come back to its original shape. You can stretch a rubber band quite a bit and when you stop stretching it comes back to the way it was. A basketball actually squashes a bit when it hits the sidewalk and when it unsquashes it bounces back up. If you stretch, twist or squash something beyond its elastic limit it will break or deform.


Imagine taking a rubber band, for example, and stretching it so much that it breaks. You’ve stretched it beyond its elastic limit and it broke. Another example, would be taking a wire pipe cleaner. If you bend it just a bit, it will bend back to its original shape. If you go to far, it stays in the new shape. You have bent it beyond its elastic limit.


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Vapor pressure and changes in state

Thursday June 15, 2017

An average can of soda at room temperature measures 55 psi before you ever crack it open. (In comparison, most car tires run on 35 psi, so that gives you an idea how much pressure there is inside the can!)


If you heat a can of soda, you’ll run the pressure over 80 psi before the can ruptures, soaking the interior of your house with its sugary contents. Still, you will have learned something worthwhile: adding energy (heat) to a system (can of soda) causes a pressure increase. It also causes a volume increase (kaboom!).
How about trying a safer variation of this experiment using water, an open can, and implosion instead of explosion?


Materials – An empty soda can, water, a pan, a bowl, tongs, and a grown-up assistant.


NOTE: If you can get a hold of one, use a beer can – they tend to work better for this experiment. But you can also do this with a regular old soda can. And no, I am not suggesting that kids should be drinking alcohol! Go ask a parent to find you one – and check the recycling bin.


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Prepare an ice bath by putting about ½” of ice water in a shallow dish. With an adult, place a few tablespoons of water in an empty soda or beer can and place the can upright in a skillet on the stove. When the can emits a think trickle of steam, grab the can with tongs and quickly invert it into the ice dish. CRACK!


Troubleshooting: The trick to making this work is that the can needs to be full of hot steam, which is why you only want to use a tablespoon or two of water in the bottom of the can. It’s alright if a bit of water is still at the bottom of the can when you flip it into the ice bath. In fact, there should be some water remaining or you’ll superheat the steam and eventually melt the can. You want enough water in the ice bath to completely submerge the top of the can.


Always use tongs when handling the heated can and make sure you completely submerge the top of the can in the icy water. The water needs to seal the hole in the top of the can so the steam doesn’t escape. Be prepared for a good, loud CRACK! when you get it right.


Why does this work? By heating up the water in the can, you’re changing the state of water from a liquid to a has (called water vapor), which drives out the air, leaving the steam inside. When inverted and cooled, the steam condenses to a small volume of liquid water (much smaller than if it was just hot air). The molecules in water vapor are a lot further apart than when they are in a liquid state. Since the air inside the can has been replaced by the steam, when it cools quickly, it creates a lower air pressure region in the can, so the air pressure surrounding the outside of the can rapidly crushes the can.


If you look really carefully as it condenses, you’ll see cold water from the bowl zoom into the can, just like when you suck water through a straw. The vacuum created int he can by the condensing steam creates a lower pressure, which pushes water into the can itself. When you suck from a straw, you’re creating a lower air pressure region in your mouth so that the surrounding air pressure pushes liquid up the straw to equalize the pressure.


Remember, high pressure always pushes!


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Click here to go to next lesson on Solids


Intermolecular Forces

Thursday June 15, 2017

Now let’s take a look at the forces between the molecules themselves. There are four main interactions which really come down to different ways of having opposite charges attract each other.


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Covalent Bonds and Polarity

Thursday June 15, 2017

A molecule is the smallest unit of a compound that still has the compound’s properties attached to it. Molecules are made up of two or more atoms held together by covalent bonds.


In the space where electrons from different atoms interact with each other, chemical bonds form. The electrons in the outermost shell are the ones that form the bonds with other atoms.


When the atoms share the electron(s), a covalent bond is formed. Electrons aren’t perfect, though, and usually an electron is more attracted to one atom than another, which forms a polar covalent bond between atoms (like in water, H2O).


While it may seem a bit random right now, with a little bit of study, you’ll find you can soon understand how molecules are formed and the shapes they choose once you figure out the types of bonds that can form.


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Let’s take an example:


Why does ice float? In the water molecule (H2O) is held together by polar covalent bonds. Water molecules are also attracted to each other by weak (hydrogen) bonds between the atoms. As water cools below 4°C, the hydrogen bonds forms a hexagonal crystal lattice (known as ‘ice’). The solid form of water is a larger structure than the liquid form, as the crystal structure has a hole in the center. In other words, ice takes up about 9% more space than liquid water, so a liter of ice weighs less than a liter water. By peeking into the molecules closely, you can explain why ice is one of the very few solids that is lighter than its liquid form.


Water is also a polar molecule, which happens because one end of the molecule has slightly more charge than the other end.


When two different kinds of atoms, like oxygen and hydrogen form a bond, one attracts the shared pair of electrons more strongly than the other. (When a bond forms between two of the same kind of atom do we assume the attraction is equal, so atoms like O2 and N2 are not polar).


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Click here to go to next lesson on Intermolecular Forces

Desalination

Thursday June 15, 2017

This experiment is for advanced students.Have you ever taken a gulp of the ocean? Seawater can be extremely salty! There are large quantities of salt dissolved into the water as it rolled across the land and into the sea. Drinking ocean water will actually make you thirstier (think of eating a lot of pretzels). So what can you do if you’re deserted on an island with only your chemistry set?


Let me show you how to take the salt out of water with this easy setup.


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Materials:


  • salt
  • water
  • alcohol burner
  • flask with one-hole stopper
  • stand with wire mesh screen
  • two 90-degree glass pipes
  • flexible tubing
  • ring stand with clamp
  • lighter with adult help


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Click here to go to next lesson on Covalent Bonds and Polarity


Rock Candy

Thursday June 15, 2017

We’re going to take two everyday materials, salt and vinegar, and use them to grow crystals by creating a solution and allowing the liquids to evaporate.  These crystals can be dyed with food coloring, so you can grow yourself a rainbow of small crystals overnight.


The first thing you need to do is gather your materials.  You will need:


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Here’s what you need:


  • 1 cup of warm water
  • 1/4 cup salt (non-iodized works better)
  • 2 teaspoons to 2 tablespoons of vinegar (you decide how much you want to use)
  • a shallow dish (like a pie plate)
  • a porous material to grow your crystals on (like a sponge)

First, mix together the salt, vinegar, and water in a cup.  (You cal alternatively boil the water on the stove and stir in as much salt as the water will dissolve.)  Add the vinegar after you turn off the heat. Next, place your sponge in a bowl and pour the solution over the sponge, submerging the sponge in the solution.  Leave out, undisturbed, until the liquids evaporate, leaving behind a sheet of crystals.



 
Download worksheet and exercises


You can add more liquid carefully to the bowl to continue the growth of your crystals for long after the first solution dries up.  Also, as your crystals grow, dot the sponge with drops of food coloring to crow various colors of crystals.


Although it takes awhile for the crystals to start growing, once they do, they will continue to grow quickly!


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Click here to go to next lesson on Desalination


Salt and Sugar Crystals

Thursday June 15, 2017

We’re going to take two everyday materials, salt and vinegar, and use them to grow crystals by creating a solution and allowing the liquids to evaporate.  These crystals can be dyed with food coloring, so you can grow yourself a rainbow of small crystals overnight.


The first thing you need to do is gather your materials.  You will need:


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Here’s what you need:


  • 1 cup of warm water
  • 1/4 cup salt (non-iodized works better)
  • 2 teaspoons to 2 tablespoons of vinegar (you decide how much you want to use)
  • a shallow dish (like a pie plate)
  • a porous material to grow your crystals on (like a sponge)

First, mix together the salt, vinegar, and water in a cup.  (You cal alternatively boil the water on the stove and stir in as much salt as the water will dissolve.)  Add the vinegar after you turn off the heat. Next, place your sponge in a bowl and pour the solution over the sponge, submerging the sponge in the solution.  Leave out, undisturbed, until the liquids evaporate, leaving behind a sheet of crystals.



 
Download worksheet and exercises


You can add more liquid carefully to the bowl to continue the growth of your crystals for long after the first solution dries up.  Also, as your crystals grow, dot the sponge with drops of food coloring to crow various colors of crystals.


Although it takes awhile for the crystals to start growing, once they do, they will continue to grow quickly!


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Click here to go to next lesson on Rock Candy


Ionic Bonds

Thursday June 15, 2017

There are different kinds of bonds that can form in a molecule. When two atoms approach each other close enough for their electron clods to interact, the electrons of one repels the electrons in the other, and the same thing happens within the nucleus of the atoms. At the same time, each atom’s negatively charged electron is attracted to the other atom’s positively charged nucleus. If the atoms still come closer, the attractive forces offset the repulsive and the energy of the atom decreases and bonds are formed – the atom sticks together. When the energy decrease is small, the bonds are van der Waals. When the energy decrease is larger, we have chemical bonds, either ionic or covalent.


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Ionic bonds generally involve metals from the left side of the periodic table that interact with nonmetals from the far right side. Look at your periodic table now – do you see the atoms near the rare gases? Those usually form ions. Covalent bonds form when elements lie closer to one anther in the periodic table. Most chemical bonds are somewhere between purely ionic and purely covalent.


Ionic compounds aren’t really real molecules. When ionic compounds are solids, they are really a structure of charged particles. When one atom accepts or donates an electron to another atom, an ionic bond is formed, like in table salt (NaCl). Do you see how there’s only 1 electron in sodium in the outermost shell? And notice how chlorine has seven, not 8 in the outermost shell? Chlorine wants to feel full (8), and sodium has only 1 out of the 8, so it donates it to chlorine. Not all atoms hold onto their valence electrons with equal strength.


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Click here to go to next lesson on Salt and Sugar Crystals


Measuring Heat

Tuesday June 13, 2017

If you’ve ever had a shot, you know how cold your arm feels when the nurse swipes it with a pad of alcohol. What happened there? Well, alcohol is a liquid with a fairly low boiling point. In other words, it goes from liquid to gas at a fairly low temperature. The heat from your body is more then enough to make the alcohol evaporate.


As the alcohol went from liquid to gas it sucked heat out of your body. For things to evaporate, they must suck in heat from their surroundings to change state. As the alcohol evaporated you felt cold where the alcohol was. This is because the alcohol was sucking the heat energy out of that part of your body (heat was being transferred by conduction) and causing that part of your body to decrease in temperature.


As things condense (go from gas to liquid state) the opposite happens. Things release heat as they change to a liquid state. The water gas that condenses on your mirror actually increases the temperature of that mirror. This is why steam can be quite dangerous. Not only is it hot to begin with, but if it condenses on your skin it releases even more heat which can give you severe burns. Objects absorb heat when they melt and evaporate/boil. Objects release heat when they freeze and condense.


Do you remember when I said that heat and temperature are two different things? Heat is energy – it is thermal energy. It can be transferred from one object to another by conduction, convection, and radiation. We’re now going to explore heat capacity and specific heat. Here’s what you do:


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You Need:


  • Balloon
  • Water
  • Matches, candle, and adult help
  • Sink


Download Student Worksheet & Exercises


1. Put the balloon under the faucet and fill the balloon with some water.


2. Now blow up the balloon and tie it, leaving the water in the balloon. You should have an inflated balloon with a tablespoon or two of water at the bottom of it.


3. Carefully light the match or candle and hold it under the part of the balloon where there is water.


4. Feel free to hold it there for a couple of seconds. You might want to do this over a sink or outside just in case!


So why didn’t the balloon pop? The water absorbed the heat! The water actually absorbed the heat coming from the match so that the rubber of the balloon couldn’t heat up enough to melt and pop the balloon. Water is very good at absorbing heat without increasing in temperature which is why it is used in car radiators and nuclear power plants. Whenever someone wants to keep something from getting too hot, they will often use water to absorb the heat.


Think of a dry sponge. Now imagine putting that sponge under a slowly running faucet. The sponge would continue to fill with water until it reached a certain point and then water started to drip from it. You could say that the sponge had a water capacity. It could hold so much water before it couldn’t hold any more and the water started dripping out. Heat capacity is similar. Heat capacity is how much heat an object can absorb before it increases in temperature. This is also referred to as specific heat. Specific heat is how much heat energy a mass of a material must absorb before it increases 1°C.


Exercises Answer the questions below:


  1. What is specific heat?
    1. The specific amount of heat any object can hold
    2. The amount of energy required to raise the temperature of an object by 1 degree Celsius.
    3. The type of heat energy an object emits
    4. The speed of a compound’s molecules at room temperature
  2. Name two types of heat energy:
  3. What type (or types) of heat energy is at work in today’s experiment?
  4. True or False: Water is poor at absorbing heat energy.
    1. True
    2. False

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What is Heat?

Tuesday June 13, 2017

They can have a thermal energy but they can’t have heat. Heat is really the transfer of thermal energy. Or, in other words, the movement of thermal energy from one object to another.


If you put an ice cube in a glass of lemonade, the ice cube melts. Which way does heat flow?


The thermal energy from your lemonade moves to the ice cube.


The movement of thermal energy is called heat. The ice cube receives heat from your lemonade. Your lemonade gives heat to the ice cube.


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Click here to go to next lesson on Measuring Heat.

Temperature

Tuesday June 13, 2017

Read the temperature from the thermometer… what do you get? This thermometer is reading in Celsius.


We’ll cover thermometers and the four temperature scales in a bit when we get to thermochemistry, but I just wanted to make sure we’re all on the same page when it comes to reading a thermometer, especially now that so many are digital and some kids may have not yet had the experience of reading a temperature scale.


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Click here to go to next lesson on What is Heat?.


Temperature and Thermometers

Tuesday June 13, 2017

First invented in the 1600s, thermometers measure temperature using a sensor (the bulb tip) and a scale. Temperature is a way of talking about, measuring, and comparing the thermal energy of objects. We use three different kinds of scales to measure temperature. Fahrenheit, Celsius, and Kelvin. (The fourth, Rankine, which is the absolute scale for Fahrenheit, is the one you’ll learn about in college.)


Mr. Fahrenheit, way back when (18th century) created a scale using a mercury thermometer to measure temperature. He marked 0° as the temperature ice melts in a tub of salt. (Ice melts at lower temperatures when it sits in salt. This is why we salt our driveways to get rid of ice). To standardize the higher point of his scale, he used the body temperature of his wife, 96°.


As you can tell, this wasn’t the most precise or useful measuring device. I can just imagine Mr. Fahrenheit, “Hmmm, something cold…something cold. I got it! Ice in salt. Good, okay there’s zero, excellent. Now, for something hot. Ummm, my wife! She always feels warm. Perfect, 96°. ” I hope he never tried to make a thermometer when she had a fever.


Just kidding, I’m sure he was very precise and careful, but it does seem kind of weird. Over time, the scale was made more precise and today body temperature is usually around 98.6°F.


Later, (still 18th century) Mr. Celsius came along and created his scale. He decided that he was going to use water as his standard. He chose the temperature that water freezes at as his 0° mark. He chose the temperature that water boils at as his 100° mark. From there, he put in 100 evenly spaced lines and a thermometer was born.


Last but not least Mr. Kelvin came along and wanted to create another scale. He said, I want my zero to be ZERO! So he chose absolute zero to be the zero on his scale.


Absolute zero is the theoretical temperature where molecules and atoms stop moving. They do not vibrate, jiggle or anything at absolute zero. In Celsius, absolute zero is -273 ° C. In Fahrenheit, absolute zero is -459°F (or 0°R). It doesn’t get colder than that!


As you can see, creating the temperature scales was really rather arbitrary:


“I think 0° is when water freezes with salt.”
“I think it’s just when water freezes.”
“Oh, yea, well I think it’s when atoms stop!”


Many of our measuring systems started rather arbitrarily and then, due to standardization over time, became the systems we use today. So that’s how temperature is measured, but what is temperature measuring?


Temperature is measuring thermal energy which is how fast the molecules in something are vibrating and moving. The higher the temperature something has, the faster the molecules are moving. Water at 34°F has molecules moving much more slowly than water at 150°F. Temperature is really a molecular speedometer.


Let’s make a quick thermometer so you can see how a thermometer actually works:


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Materials:


  • plastic bottle
  • straw
  • hot glue or clay
  • water
  • food coloring
  • rubbing alcohol
  • index card and pen


When something feels hot to you, the molecules in that something are moving very fast. When something feels cool to you, the molecules in that object aren’t moving quite so fast. Believe it or not, your body perceives how fast molecules are moving by how hot or cold something feels. Your body has a variety of antennae to detect energy. Your eyes perceive certain frequencies of electromagnetic waves as light. Your ears perceive certain frequencies of longitudinal waves as sound. Your skin, mouth and tongue can perceive thermal energy as hot or cold. What a magnificent energy sensing instrument you are!


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Click here to go to next lesson on Temperature.

Spectral Chemical Analysis Part 2

Tuesday June 13, 2017

This experiment is for advanced students. There are many different elements inside of a star. But they are so far away that we can’t get close enough to study them… or can we? By studying the special light signature (called “spectral lines”) astronomers can figure out not only which element, but also the approximate temperature and density of the element within the star, in addition to getting an idea of what the magnetic fields look like, which tells us about stellar wing and what the planets might be doing around the star, or if there might be another companion star.


Spectroscopy is a very complicated science, so let’s get started by actually doing it, and we’ll figure out what’s going on along the way.


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Materials:



If you are making your own spectrometer, you can make a simple spectrometer or the more advanced calibrated spectrometer.


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Click here for Homework Problem Set #6

Spectral Chemical Analysis

Tuesday June 13, 2017

You’re going to try to determine what is happening during the flame test when you see different colors. Think about what particles are found in the chemicals you’re using, and why the different chemicals emit different colors of light? Where else have you seen colorful light emissions?


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Click here to go to next lesson on Spectral Chemical Analysis Part 2.

Calibrated Spectrometer

Tuesday June 13, 2017

Ever play with a prism? When sunlight strikes the prism, it gets split into a rainbow of colors. Prisms un-mix the light into its different wavelengths (which you see as different colors). Diffraction gratings are tiny prisms stacked together.

When light passes through a diffraction grating, it splits (diffracts) the light into several beams traveling at different directions. If you’ve ever seen the ‘iridescence’ of a soap bubble, an insect shell, or on a pearl, you’ve seen nature’s diffraction gratings.

Scientist use these things to split incoming light so they can figure out what fuels a distant star is burning. When hydrogen burns, it gives off light, but not in all the colors of the rainbow, only very specific colors in red and blue. It’s like hydrogen’s own personal fingerprint, or light signature.

While this spectrometer isn't powerful enough to split starlight, it's perfect for using with the lights in your house, and even with an outdoor campfire.  Next time you're out on the town after dark, bring this with you to peek different types of lights - you'll be amazed how different they really are. You can use this spectrometer with your Colored Campfire Experiment also.

SPECIAL NOTE: This instrument is NOT for looking at the sun. Do NOT look directly at the sun. But you can point the tube at a sheet of paper that has the the sun’s reflected light on it.

Here's what you do:

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Download Student Worksheet & Exercises

You will need:

  • cardboard box (ours is 10" x 5" x 5", but anything close to this will work fine)
  • linear diffraction grating (you can order one here)
  • 2 razor blades (with adult help)
  • masking tape
  • ruler
  • photocopy of a ruler (or sketch a line with 1 through 10 cm markings on it, about 4cm wide)

1. Using a small box, measure 4.5 cm from the edge of the box. Starting here, cut a hole for the double-razor slit that is 1.5 cm wide 3 cm long.

2. From the other edge (on the same side), cut a hole to hold your scale that is 11 cm wide and 4 cm tall.

3. Print out the scale and attach it to the edge of the box.

4. Very carefully line up the two razors, edge-to-edge to make a slit and secure into place with tape.

5. On the opposite side of the box, measure over 3 cm and cut a hole for the diffraction grating that is 4 cm wide and 3 cm tall.

5. Tape your diffraction grating over the hole.

Aim the razor slit at a light source such as a fluorescent light, neon sign, sunset, light bulb, computer screen, television, night light, candle, fireplace… any light source you can find. Put the diffraction grating up to your eye and look at the inner scale.  Move the spectrometer around until you can get the rainbow to be on the scale inside the box.

How to Calibrate the Spectrometer with the Scale Inside your box is a scale in centimeters. Point your slit to a fluorescent bulb, and you'll see three lines appear (a blue, a green, and a yellow-orange line). The lines you see in the fluorescent bulb are due to mercury superimposed on a rainbow continuous spectrum due to the coating. Each of the lines you see is due to a particular electron transition in the visible region of Hg (mercury). The blue line (435 nm), the green line (546 nm), and the yellow orange line (579 nm). (If you look at a sodium vapor street light you'll see a yellow line (actually 2 closely spaced) at 589 nm.)

Step 1. Line the razor slits along the length of the fluorescent tube to get the most intense lines. Move the box laterally (the lines will move due to parallax shift).

Step 2. Take scale readings at the extreme of the these movements and take the average for the scale reading. For instance, if the blue line averages to the 8.8 cm value, this corresponds to the 435 nm wavelength. Do this for the other 2 lines.

Step 3. On graph paper, plot the cm ( the ruler scale values) on the vertical axis and the wavelength (run this from 400-700 nm) on the horizontal axis. Draw the best straight lines thru the 3 points (4 lines if you use the Na (sodium) street lamp). You've just calibrated the spectrometer.

Step 4. Line the razor slits up with another light source.  Notice which lines appear and where they are on your scale.  Find the value on your graph paper. For example, if you see a line appear at 5.5 cm, use your finger to follow along to the 5.5 cm until you hit the best-fit line, and then read the corresponding value on the wavelength axis. You now have the wavelength for the line you've just seen!

Notes on Calibration and Construction: If you swap out different diffraction gratings, you will have to re-calibrate. If you make a new spectrometer, you will have to re-calibrate to the Hg (mercury) lines for each new spectrometer. If you do remake the box, use a scale that is translucent so you can see the numbers. If you use a clear plastic ruler, it may let in too much light from the outside making it difficult to read the emission line.

What other light sources work? Use your spectrometer to look at computer screens, laptops, night lights, neon lights, candles, campfires, fluorescent lights, incandescent lights, LEDs, stoplights, street lights, and any other light sources you can find. When you walk down town at night and look at various "neon" signs. Ne (neon) is a real burner! Do this with a friend who is willing to vouch for your sanity.

Question: What happens when you aim a laser through a diffraction grating? (See picture above - can you find the two dots on either side of the main later dot?)

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Click here to go to next lesson on Spectral Chemical Analysis.


Spectrometer

Monday June 12, 2017

Did you aim your razor slit at a light source such as a fluorescent light, neon sign, sunset, light bulb, computer screen, television, night light, candle, fireplace… ? Make sure that the diffraction grating does right up to your eye.  Move the spectrometer around until you can get the rainbow to be on the scale inside the tube.


Once you’ve got the hang of it, you might be wondering, wow – cool… but what am I looking at exactly? Ok – so those lines you saw inside the tube – those are spectral lines. Can you see how there are brighter lines? Which frequencies are those? Well we need a ruler to measure those. Can you see how if we lined up a ruler as could tell what the frequencies are?


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What other light sources work? Use your spectrometer to look at computer screens, laptops, night lights, neon lights, candles, campfires, fluorescent lights, incandescent lights, LEDs, stoplights, street lights, and any other light sources you can find. When you walk down town at night and look at various “neon” signs.


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Click here to go to next lesson on simple.

Simple

Monday June 12, 2017

spectrometer2Spectrometers are used in chemistry and astronomy to measure light. In astronomy, we can find out about distant stars without ever traveling to them, because we can split the incoming light from the stars into their colors (or energies) and “read” what they are made up of (what gases they are burning) and thus determine their what they are made of. In this experiment, you’ll make a simple cardboard spectrometer that will be able to detect all kinds of interesting things!


SPECIAL NOTE: This instrument is NOT for looking at the sun. Do NOT look directly at the sun. But you can point the tube at a sheet of paper that has the sun’s reflected light on it.


Usually you need a specialized piece of material called a diffraction grating to make this instrument work, but instead of buying a fancy one, why not use one from around your house?  Diffraction gratings are found in insect (including butterfly) wings, bird feathers, and plant leaves.  While I don’t recommend using living things for this experiment, I do suggest using an old CD.


CDs are like a mirror with circular tracks that are very close together. The light is spread into a spectrum when it hits the tracks, and each color bends a little more than the last. To see the rainbow spectrum, you’ve got to adjust the CD and the position of your eye so the angles line up correctly (actually, the angles are perpendicular).


You’re looking for a spectrum (the rainbow image at left) – this is what you’ll see right on the CD itself. Depending on what you look at (neon signs, chandeliers, incandescent bulbs, fluorescent bulbs, Christmas lights…), you’ll see different colors of the rainbow. For more about how diffraction gratings work, click here.


Materials:


  • old CD
  • razor
  • index card
  • cardboard tube

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Download Student Worksheet & Exercises


Find an old CD and a cardboard tube at least 10 inches long.  Cut a clean slit less than 1 mm wide in an index card or spare piece of cardboard and tape it to one end of the tube.  Align your tube with the slit horizontally, and on the top of the tube at the far end cut a viewing slot about one inch long and ½” inch wide.  Cut a second slot into the tube at a 45 degree angle from the vertical away from the viewing slot.  Insert the CD into this slot so that it reflects light coming through the slit into your eye (viewing slot).


Aim the 1 mm slit at a light source such as a fluorescent light, neon sign, sunset, light bulb, computer screen, television, night light, candle, fireplace… any light source you can find.  Look through the open hole at the light reflected off the compact disk (look for a rainbow in most cases) inside the cardboard tube.


Troubleshooting: This is a quick and easy way to bypass the need for an expensive diffraction grating. Use your spectrometer to look at computer screens, laptops, night lights, neon lights, candles, campfires, fluorescent lights, incandescent lights, LEDs, stoplights, street lights, and any other light sources you can find, even the moon through a telescope.


Exercises


  1. Name three more light sources that you think might work with your spectroscope.
  2.   Why is there a slit at the end of the tube instead of leaving it open?

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Click here to go to next lesson on Calibrated.


Cold Light

Monday June 12, 2017

Glow sticks generate light with very little heat, just like the glow you see from fireflies, jellyfish, and a few species of fungi. Chemiluminescence means light that comes from a chemical reaction. When this happens in animals and plants, it’s called bioluminescence.


In a glow stick, when you bend it to activate it, you’re breaking a little glass tube inside which contains hydrogen peroxide (H2O2). The tube itself is filled with another chemical (phenyl oxalate ester and a fluorescent dye) that is kept separate from the H2O2, because as soon as they touch, they begin to react. The dye in the light stick is what gives the light its color.


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Materials:



You’ll need a really dark room to see this reaction take place, as the amount of light it gives off is low, but it’s still there! Allow your eyes to adjust to the darkness for about 10 minutes, and you’ll definitely see a blue glow in the liquid.


The light comes from the copper sulfate reacting with the luminol, and will continue until one of the reactants is used up.


For advanced students, you can do this experiment with Cold Light.
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Click here to go to next lesson on Spectrometer.

Fluorescence, Phosphorescence, and Chemiluminescence

Monday June 12, 2017

Which one of these things you see on the screen now is radioactive? Most kids think that anything that glows must be radioactive, but it turns out that there’s a lot of things that glow that aren’t radioactive at all. Many minerals (called phosphors) glow after being exposed to sunlight which contains UV light. In 1897, Henri Becquerel was studying phosphorescence when he accidentally discovered radioactivity. Naturally radioactive elements emit energy without absorbing it first. Let me explain…


Cold light refers to the light from a glow stick, called luminescence. A chemical reaction (chemiluminescence) starts between two liquids, and the energy is released in the form of light. On the atomic scale, the energy from the reaction bumps the electron to a higher shell, and when it relaxes back down it emits a photon of light. Glow sticks generate light with very little heat, just like the glow you see from fireflies, jellyfish, and a few species of fungi. Chemiluminescence means light that comes from a chemical reaction.
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Fluorescence is what you see on those dark amusement-park rides that have UV lights all around to make objects glow. The object (like a rock) will absorb the UV light and remit a completely different color. The light strikes the electron and bumps it up a level, and when the electron relaxed back down, emits a photon, a light particle. Can you find the image with the glowing rocks? There’s two of them – one with the lights on and one with the lights off. Right – on the left side. The reason stuff glows is that fluorescent objects absorb the UV light and then spit it back almost instantaneously. Some of that energy gets lost during that process, and that changes the wavelength of the light, which makes this light visible and causes the material to appear to ‘glow’.


Sometimes things glow even after you turn off the UV light source. Phosphorescence light is the ‘glow-in-the-dark’ kind you have to ‘charge up’ with a light source. This delayed afterglow happens because the electron gets stuck in a higher energy state. Lots of toys and stick-on stars are coated with phosphorescent paints. Those are like the stars and planets you see in the middle of the slide. Atoms continue to emit light even after the electrons return to their normal energy states. While it looks like seconds to minutes that the glow lasts, some samples have been found to phosphoresce for years using highly sensitive photographic methods. Only a few minerals phosphoresce, such as calcite from Terlingua, Texas.


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Click here to go to next lesson on Cold Light.

Photoelectric effect

Monday June 12, 2017
Photoelectric EffectEinstein received a Nobel Prize for figuring out what happens when you shine blue light on a sheet of metal.  When he aimed a blue light on a metal plate, electrons shot off the surface. (Metals have electrons which are free to move around, which is why metals are electrically conductive. More on this in Unit 10).

When Einstein aimed a red light at the metal sheet, nothing happened.  Even when he cranked the intensity (brightness) of the red light, still nothing happened.  So it was the energy of the light (wavelength), not the number of photons (intensity) that made the electrons eject from the plate. This is called the ‘photoelectric effect’. Can you imagine what happens if we aim a UV light (which has even more energy than blue light) at the plate?

This photoelectric effect is used by all sorts of things today, including solar cells, electronic components, older types of television screens, video camera detectors, and night-vision goggles.

This photoelectric effect also causes the outer shell of orbiting spacecraft to develop an electric charge, which can wreck havoc on its internal computer systems.

A surprising find was back in the 1960s, when scientists discovered that moon dust levitated through the photoelectric effect. Sunlight hit the lunar dust, which became (slightly) electrically charged, and the dust would then lift up off the surface in thin, thread-like fountains of particles up ¾ of a mile high.

[am4show have='p9;p58;' guest_error='Guest error message' user_error='User error message' ] Materials:
  • soda or steel can
  • paper clip
  • sand paper
  • tinsel (or aluminum foil and scissors)
  • tape
  • foam cup
  • PVC pipe (any size)
  • brown paper bag
  • UV shortwave lamp (sometimes called a "germ-free portable lamp")


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Click here to go to next lesson on Fluorescence, Phosphorescence, and Chemiluminescence.

 

Grade Levels

Monday June 12, 2017
PRE-K & K
First Grade
Second Grade
Third Grade
Fourth Grade
Fifth Grade
Sixth Grade
Seventh Grade
Eighth Grade
High School (Advanced)
Teaching Resources
Science Fair Projects
These are the scientific concepts students learn, separated by grade level according to both the national standards for science and Aurora’s personal experience in working with kids for nearly two decades. The scientific concepts are organized into categories within each grade level. You’ll find some areas span more than one grade level, so you will see some experiments listed for multiple grade levels.

PRE-K & K

Material properties, introduction to forces and motion, plants and animals, and basic principles of earth science.

First Grade

States of matter, weather, sound energy, light waves, and experimenting with the scientific method.

Second Grade

Chemical reactions, polymers, rocks and minerals, genetic traits, plant and animal life cycles, and Earth's resources.

Third Grade

Newton's law of motion, celestial objects, telescopes, measure the climate of the Earth and discover the microscopic world of life.

Fourth Grade

Electricity and magnetism, circuits and robotics, rocks and minerals, and the many different forms of energy.

Fifth Grade

Chemical elements and molecules, animal and plant biological functions, heat transfer, weather, planetary and solar astronomy.

Sixth Grade

Heat transfer, convetion currents, ecosystems, meteorology, simple machines, and alternative energy.

Seventh Grade

Cells, genetics, DNA, kinetic and potential, thermal energy, light and lasers, and biological structures.

Eighth Grade

Acceleration, forces projectile motion chemical reactions, deep space astronomy, and the periodic table.

High School (Advanced)

Alternative energy, astrophysics, robotics, chemistry, electronics, physics and more. For high school & advanced 5-8th students.

Teaching Resources

Tips and tricks to getting the science education results you want most for your students.

Science Fair Projects

Hovercraft, Light Speed, Fruit Batteries, Crystal Radios, R.O.V Underwater Robots and more!


Atomic spectra of hydrogen and energy levels

Monday June 12, 2017
This is a recording of a recent live class I did with an entire high school astronomy class. I've included it here so you can participate and learn, too! Light is energy that can travel through space. How much energy light has determines what kind of wave it is. It can be visible light, x-ray, radio, microwave, gamma or ultraviolet. The electromagnetic spectrum shows the different energies of light and how the energy relates to different frequencies, and that's exactly what we're going to cover in class. We're going to talk about light, what it is, how it moves, and it's generated, and learn how astronomers study the differences in light to tell a star's atmosphere from  millions of miles away. I usually give this presentation at sunset during my live workshops, so I inserted slides along with my talk so you could see the pictures better. This video below is long, so I highly recommend doing this with friends and a big bowl of popcorn. Ready? [am4show have='p8;p9;p96;' guest_error='Guest error message' user_error='User error message' ] Materials:
  • Hair (one strand)
  • Tape
  • Pencil
  • Ruler or yardstick
  • Paper
  • Calculator
  • Red laser
  • Flashlight
  • Glass of water
  • Large chocolate bar
  • Microwave
  • Plate
  • Orange highlighter
  • Diffraction grating OR use an old CD
  • Print out this worksheet to fill in as we go along!
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Click here to go to next lesson on Photons and Energy.


Properties of light and study of waves

Monday June 12, 2017

Energy can take one of two forms: matter and light (called electromagnetic radiation). Light is energy that can travel through space. When you feel the warmth of the sun on your arm, that’s energy from the sun that traveled through space as infrared radiation (heat). When you see a tree or a bird, that’s light from the sun that traveled as visible light (red, orange… the whole rainbow) reflecting and bouncing off objects to get to your eye. Light can travel through objects sometimes… like the glass in a window.


Light can take the form of either a wave or a particle, depending on what you’re doing with it. It’s like a reversible coat – fleece on the inside, windbreaker on the outside. It can adapt to whatever environment you put it in.
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When Einstein aimed a red light at the metal sheet, nothing happened.  Even when he cranked the intensity (brightness) of the red light, still nothing happened.  So it was the energy of the light (wavelength, or color), not the number of photons (brightness or intensity) that made the electrons eject from the plate. This is called the ‘photoelectric effect’. A UV light makes ever more electrons jump off the plate!


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Click here to go to next lesson on Atomic spectra of hydrogen and energy levels.

Alpha Particle Detector

Monday June 12, 2017

This experiment is for advanced students. Here is another way to detect cosmic rays, only this time you’ll actually see the thin, threadlike vapor trails appear and disappear. These cobwebby trails are left by the particles within minutes of creating the detector. (Be sure to complete the Cosmic Ray Detector first!)


In space, there are powerful explosions (supernovas) and rapidly-spinning neutron stars (pulsars), both of which spew out high energy particles that zoom near the speed of light. Tons of these particles zip through our atmosphere each day. There are three types of particles: alpha, beta, and gamma.


Did you know that your household smoke alarm emits alpha particles? There’s a small bit (around 1/5000th of a gram) of Americium-241, which emits an alpha particle onto a detector. As long as the detector sees the alpha particle, the smoke alarm stays quiet. However, since alpha particles are easy to block, when smoke gets in the way and blocks the alpha particles from reaching the detector, you hear the smoke alarm scream.


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Alpha particles are actually high speed helium nuclei (which is two protons and two neutrons stuck together). They were named long before we knew what they were of, and the name stuck. Alpha particles are pretty heavy and slow, and most get stopped by just about anything, a sheet of paper or your skin. Because of this, alpha particles are not something people get excited about, unless you actually eat the smoke detector.


Both brick buildings as well as people emit beta particles. Beta particles are actually high speed electrons or positrons (a positron is the antimatter counterpart to the electron), and they are quick, fast, and light. You can stop a beta particle by holding up a thin sheet of plastic or tinfoil.


When you hold the jar in your hands, you warm it slightly and cause the air inside to get saturated with alcohol vapor. When the alpha particles (cosmic rays) zip through this portion of the jar, they quickly condense the alcohol and create spider-webby vapor trails. Try using a magnet to deflect the cosmic rays.


Here’s what you need:


  • rubbing alcohol
  • clean glass jar
  • black felt
  • hot glue gun
  • magnet
  • flashlight
  • scissors
  • dry ice and heavy gloves for handling the dry ice (and adult help)


 
Download Student Worksheet & Exercises


You will be making a special cloud chamber that holds alcohol gas inside. When you hold the jar in your hands, you warm it slightly and cause the air inside to get saturated with alcohol vapor. When the alpha particles (cosmic rays) zip through this portion of the jar, they quickly condense the alcohol and create spider-webby vapor trails. Kind of like when a jet flies through the air – you can’t always see the jet, but the cloud vapor trails streaming out behind stay visible for a long time. In our case, the vapor trails are visible for only a couple of seconds.


  1. Cut your felt to the size of the bottom of your jar.  Glue the felt to the bottom of the jar.
  2. Cut out another felt circle the size of the lid and glue it to the inside surface of the lid.
  3. Cut a third felt piece, about 2 inches wide, and line the inside circumference of the jar, connecting it with the bottom felt. Glue it into place.
  4. Strap goggles on your face. No exceptions.
  5. Very carefully pour a tablespoon or two of the highest concentration of rubbing alcohol onto the felt in the jar. You don’t need much. Swirl it around to distribute it evenly. Do the same for the lid. All the felt pieces should be thoroughly saturated. Cap the jar and leave it for ten minutes while you explain about dry ice (see safety precautions above under Important Project Considerations.
  6. Your teacher is coming around with the dry ice. Remove the lid and your teacher will place a small piece of dry ice right on the lid. Invert the jar right over the lid. Leave the jar upside down.
  7. DO NOT SCREW ON THE CAP TIGHTLY! Leave it loose to allow the pressure to escape.
  8. Sit and wait and watch carefully for the tiny, thin, threadlike vapor trails.
  9. What do you think the magnet is for? (Hint: Keep it outside the jar.)

What’s Going On?

Cosmic rays have a positive charge, as the particles are usually protons, though one in every 100 is an electron (which has a negative charge) or a muon (also a negative charge, but 200 times heavier than an electron).  On a good day, your cosmic ray indicator will blip every 4-5 seconds.  These galactic cosmic rays are one of the most important problems for interplanetary travel by crewed spacecraft.


Most cosmic rays zoom to us from extrasolar sources (stars that are outside our solar system but inside our galaxy) such as high-energy pulsars, grazing black holes, and exploding stars (supernovae).  We’re still figuring out whether some cosmic rays started from outside our own galaxy. If they are from outside our galaxy, it means that we’re getting stuff from quasars and radio galaxies, too!


Cosmic rays are fast-moving, high-energy, charged particles. The particles can be electrons, protons, the nucleus of a helium atom, or something else. In our case, the cosmic rays we’re detecting are “alpha particles.” Alpha particles are actually high-speed helium nuclei (helium nuclei are two protons and two neutrons stuck together). They were named “alpha particles” long before we knew what they were made of, and the name just kind of stuck.


Did you know that your household smoke alarm emits alpha particles? Most smoke detectors contain a small bit (around 1/5,000th of a gram) of Americium-241, which emits an alpha particle onto a detector. As long as the detector sees the alpha particle, the smoke alarm stays quiet. However, since alpha particles are easy to block, when smoke gets in the way and blocks the alpha particles from reaching the detector, you hear the smoke alarm scream.


Alpha particles are pretty heavy and slow, and most get stopped by just about anything, like a sheet of paper or your skin. Because of this, alpha particles are not something people get very excited about, unless you actually eat the smoke detector and ingest the material (which is not recommended).


Both brick buildings as well as people emit beta particles. Beta particles are actually high-speed electrons or positrons (a positron is the antimatter counterpart to the electron), and they are quick, fast, and light. When an electron hit the foil ball, it traveled down and charged the foil leaves, which deflected a tiny bit inside the electroscope. A beta particle has a little more energy than an alpha particle, but you can still stop it in its tracks by holding up a thin sheet of plastic (like a cutting board) or tinfoil.


Important Project Considerations:


After creating your detector: You can bring your alpha particle detector near a smoke alarm, an old glow-in-the-dark watch dial or a Coleman lantern mantel. You can go on a hunt around your house to find where the particles are most concentrated. If you have trouble seeing the trails, try using a flashlight and shine it on the jar at an angle.


You will also be working with dry ice. The dry ice works with the alcohol to get the vapor inside the jar at just the right temperature so it will condense when hit with the particles. Note that you should NEVER TOUCH DRY ICE WITH YOUR BARE HANDS. Always use gloves and tongs and handle very carefully. Keep out of reach of children – the real danger is when kids think the ice is plain old water ice and pop it in their mouth.


If your dry ice comes in large blocks, the easiest way to break a large chunk of dry ice into smaller pieces is to insert your hands into heavy leather gloves, wrap the dry ice block in a few layers of towels, and hit with a hammer. Make sure you wrap the towels well enough so that when the dry ice shatters, it doesn’t spew pieces all over. Use a metal pie plate to hold the chunks while you’re working with them. Store unused dry ice in a paper bag in a cooler or the coldest part of the freezer. Dry ice freezes at -109 degrees Fahrenheit. Most freezers don’t get that cold, so expect your dry ice to disappear soon.


TIP: You can bring your alpha particle detector near a smoke alarm, an old glow-in-the-dark watch dial or a Coleman lantern mantel. You can go on a hunt around your house to find where the particles are most concentrated. If you have trouble seeing the trails, try using a flashlight and shine it right on the jar.


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Click here to go to next lesson on Properties of light and study of waves.


Radioactive Substances

Monday June 12, 2017

Naturally radioactive elements emit energy without absorbing it first. Fluorescence for example – the atom absorbs a photon before emitting another photon. You have to “charge it up” or mix chemicals together before light comes out. With radioactive materials, they emit energy on their own, sometimes in the form of light, but sometimes they emit other particles. Let me explain.


Chemical reactions usually deal with only electron or atom exchanges. Nuclear reactions deal with changes inside the nucleus of an atom.
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Click here to go to next lesson on Alpha Particle Detector.

Ionization Energy

Monday June 12, 2017

Ionization energy is the energy needed to remove electrons from an atom.


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Click here to go to next lesson on Radioactive Substances.

Table Arrangement based on Electronic Properties

Monday June 12, 2017

The periodic table is more like a filing cabinet that tells you everything about the structure of the atom, its properties and how it behave in chemical reactions. With just a quick glance, you will soon be able to tell how the electrons are organized around the nucleus and also predict how the atom will interact with others.


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Click here to go to next lesson on Ionization Energy.

Valence electrons and Lewis dot structures

Monday June 12, 2017

The number of electrons in the outermost shell tells you how reactive the atom is because it tells you how many it needs to feel full, or how many it can lose. Valence electrons are the highest energy and furthest out electrons. In general, elements are less reactive when their outermost shell is full.


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Click here to go to next lesson on Alkali Metals here.

Measure a Molecule

Monday June 12, 2017

Molecules are the building blocks of matter.


You’ve probably heard that before, right? But that does it mean? What does a molecule look like? How big are they?


While you technically can measure the size of a molecule, despite the fact it’s usually too small to do even with a regular microscope, what you can’t do is see an image of the molecule itself. The reason has to do with the limits of nature and wavelengths of light, not because our technology isn’t there yet, or we’re not smart enough to figure it out. Scientists have to get creative about the ways they do about measuring something that isn’t possible to see with the eyes.


Here’s a cool experiment you can do that will approximate the size of a molecule. Here’s what you need:


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Materials:


  • liquid dish soap
  • chalk dust
  • medicine dropper
  • pie pan
  • ruler
  • water
  • calculator


 
Download student worksheet and exercises here!


  1. Place water in the pie pan and sprinkle in the chalk dust. You want a light, even coating on the surface.
  2. Place dish soap inside the medicine dropper and hold it up.
  3. Squeeze the medicine dropper carefully and slowly so that a single drop forms at the tip. Don’t let it fall!
  4. Hold the ruler up and measure the drop. Record this in your data sheet.
  5. Hold the tip of the dropper over the pie pan near the surface and let it drop onto the water near the center of the pie pan.
  6. Watch it carefully as it spreads out to be one molecule thick!
  7. Quickly measure and record the diameter of the layer of the detergent on your data sheet.
  8. Use equations for sphere and cylinder volume to determine the height (which we assume to be one molecule thick) of the soap when it’s spread out. That’s the approximate width of the molecule!

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Click here to go to next lesson on Valence electrons and Lewis dot structures.


Electron configuration

Monday June 12, 2017

One of the dreams of early chemists was to figure out how to transform lead into gold. Lead has 82 protons in its core whereas gold contains only 79. So conceivably all you’d need to do is remove three protons and presto! So how do you do that? Since protons can’t be stripped off with a chemical reaction, you need to smack it hard with something to knock off just the right amount. Lead, however, if a very stable element, so it’s going to require a lot of energy to remove three protons. How about a linear accelerator?


In a linear accelerator, a charged particle moves through a series of tubes that are charged by electrical and/or magnetic fields. The accelerated particle smacks the target, knocking free protons or neutrons and making a new element (or isotope). Glenn Seaborg (I actually met him!), 1951 Nobel Laureate in Chemistry, actually succeeded in transmuting a tiny quantity of lead into gold in 1980. He actually discovered (or helped discover) 10 elements on the periodic table, 100 new isotopes, and while he was still living (which usually doesn’t happen), they named an element after him (Seaborgium – 106).


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The strong force. Well, actually the residual strong force. This force is the glue that sticks the nucleus of an atom together, and is one of the strongest force we’ve found (on its own scale – it’s not felt at all beyond 1 femtometer 10-15m – outside the nucleus). This force binds the protons and neutrons together and is carried by tiny particles called pions. When you split apart these bonds, the energy has to go somewhere… which is why fission is such a powerful process.
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Click here to go to next lesson on Measure a Molecule.


Quantum Model of the Atom

Monday June 12, 2017

The Bohr model is useful when we want to tell how reactive an element is, but it doesn’t really work to explain how the electrons are organized around the nucleus. The quantum model is the one used today by scientists.


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Click here to go to next lesson on Electron configuration.

Bond energies

Monday June 12, 2017
Atoms are held together by bonds, and bonds take energy, so an atom that is bonded has less energy than if it was free floating around on its own. Energy is required to break a bond (bond energy). Energy is released when a bond is created. (We’ll use this idea again later when we talk about Lewis Dot structures.) Each molecule has its own bond energy which you can look up in a table in your chemistry book. For example, C-H bonds take about 100kcal of energy to break 1 mol of C-H bonds, so you’ll find bond energies listed in kcal per mol. If you look up C-C bonds, you’ll find 80 kcal/mol. And a double C-C bond is 145 kcal per mol.

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Here is a second video that shows more details and examples about the bond energies of atoms:


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Click here for Homework Problem Set #5


Fire Orange

Monday June 12, 2017

A combustion reaction gives off energy, usually in the form of heat and light.  The reaction itself includes oxygen combining with another compound to form water, carbon dioxide, and other products.


A campfire is an example of wood and oxygen combining to create ash, smoke, and other gases. Here’s the reaction for the burning of methane (CH4) which gives carbon dioxide (CO2) and water (H2O):


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CH4 + 2 O2 –> CO2 + 2 H2O



Ok – so here are the steps from the video.


  • First, cut off a strip of citrus fruit. It can be an orange, lemon, lime, tangerine, or grapefruit.
  • Do you see those little holes in the peel? They have oil inside of them.
  • Light a candle.
  • Pinch the peel between your fingers, with peel side toward the flame. You want to squirt a tiny amount of oil from the peel or rind toward the flame

The oil from citrus fruits is very flammable. When you squeeze the oil out of the fruit peel it vaporizes enough that you can flash your flame. The flash point (temp that the oil will ignite) of the oil is 122 deg F. A candle flame is about 2600 degree F. (If it doesn’t work, heat up the peel side over the flame for a few seconds first, to get those tiny pockets of oil heated up and ready to burst.)


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Click here to go to next lesson on Bond energies.


Detonating Bubbles

Monday June 12, 2017

This experiment is for advanced students.


Zinc (Zn), is a metal and it is found as element #30 on the periodic table. We need a little zinc to keep our bodies balanced, but too much is very dangerous.


Zinc is just like the common, everyday substance that we all know as di-hydrogen monoxide (which is the chemical name for water). We need water to survive, but too much will kill us.


DHMO: In chemistry, “Di” equals the number 2; hydrogen is H; mono equals the number one; and oxide is derived from oxygen, and its symbol is O. Put these together and you have Di-hydrogen (H2), and mono oxygen (O). Put them together, what do you have? Water!


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Materials:


  • Goggles
  • Gloves
  • Test tube rack
  • 3 test tubes
  • Burner
  • Lighter
  • Zinc powder (Zn) (MSDS)
  • Calcium hydroxide (Ca(OH)2 (MSDS)
  • Rubber tubing
  • Measuring spoon
  • Solid rubber stopper
  • Pan
  • Water
  • Chemistry stand
  • Test tube holder
  • 90o glass tubing
  • One-hole rubber stopper
  • Evaporating dish
  • Dish soap
  • Wood splint
  • Measuring syringe

Be careful of the hot test tubes! It may not look hot, but don’t find out the hard way. If a chemist wants to know if something is hot, he places the back of his hand near the surface. If he feels heat, he concludes that it is hot. That’s the same way we test a person’s forehead for a fever. The back of your hand is more sensitive than the front.


Zinc, zinc oxide, and calcium hydroxide are dangerous chemicals. Use your safety equipment. Dispose of the residue in the test tube in the outside garbage.


We will be creating hydrogen gas by making a heterogeneous mixture of zinc powder and calcium hydroxide and heat it. The hydrogen bubbles into test tube in a water bath. When we mix our test tube of hydrogen with the air the room, the hydrogen burns…it actually explodes. Our amounts are small, but you will witness a cool, small, explosion.


In the second part of the lab we will again create hydrogen. This time, we have a tricky way to add oxygen to the hydrogen and we are able to create a ration of 2 parts hydrogen to 1 part oxygen. This is the perfect ratio to make the most explosive mixture of hydrogen and oxygen. The explosion here is very cool.


C3000: Experiment 76-78


Download Student Worksheet & Exercises


Here’s what’s going on in this experiment:


In the first part of the lab we produce hydrogen by combining two dry chemicals and heating them. Now two things will happen. Calcium hydroxide, when heated, produces water.


Ca(OH)2 –> CaO + H2O


Calcium hydroxide, when heated, produces calcium oxide and water. This is an oxidation reaction because the calcium oxidizes….combines with the oxygen and releases the other elements.


Next, Zinc will react with water created by calcium hydroxide. As the Ca(OH)2 is heated and turns to water and calcium oxide, the zinc then reacts and produces zinc oxide and hydrogen gas.


Zn + H2O –> ZnO + H2


Zinc when heated in the presence of water, produces zinc oxide and hydrogen gas. This is a single replacement reaction as oxygen kicks out hydrogen and replaces it with zinc.


Here’s the safety information for the products of the reaction:


Cleanup: Clean everything thoroughly after you are finished with the lab. After cleaning with soap and water, rinse thoroughly. Chemists use the rule of “three” in cleaning glassware and tools. After washing, chemists rinse out all visible soap and then rinse three times more. Dry all equipment.


Storage: Place all chemicals, cleaned tools, and glassware in their respective storage places.


Disposal: Dispose of all solid waste in the outside garbage. Liquids can be washed down the drain.


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Click here to go to next lesson on Fire Orange.


What is Fire?

Monday June 12, 2017

What state of matter is fire? Is it a liquid? I get that question a LOT, so let me clarify. The ancient scientists (Greek, Chinese… you name it) thought fire was a fundamental element. Earth, Air Water, and Fire (sometimes Space was added, and the Chinese actually omitted Air and substituted Wood and Metal instead) were thought to be the basic building blocks of everything, and named it an element. And it’s not a bad start, especially if you don’t have a microscope or access to the internet.


Today’s definition of an element comes from peeking inside the nucleus of an atom and counting up the protons. In a flame, there are lots of different molecules from NO, NO2, NO3, CO, CO2, O2, C… to name a few. So fire can’t be an element, because it’s made up of other elements. So, what is it?


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Fire is a combination of different gases and hot plasma. It’s a complicated exothermic (gives off heat) chemical reaction that releases a lot of heat and light (you can feel and see the flame). You need three things for a flame: oxygen, fuel, and a spark. When you take away one of these three, you snuff the flame and stop the chemical reaction. You start with fuel (usually contains carbon), and add oxygen to get carbon dioxide, carbon monoxide, nitric oxide, and many other gases and leftover ash. Most flames are hot enough to heat the gas mixture to create tiny bits of plasma within the flame, so fire is actually involved in two states of matter.


In this experiment, we’re going to see how you can protect a surface from burning using water. Are you ready?


Materials:


  • Shallow baking dish
  • Tongs
  • Rubbing Isopropyl Alcohol (50-91%)
  • Water (omit if using 50-70% alcohol)
  • Dollar bill
  • Fire extinguisher
  • Adult help


 
Download Student Worksheet & Exercises


What’s going on? Alcohol burns with a slightly blue and orange flame (as shown in the video). The secret to keeping the dollar bill from burning is the water you mixed in with the alcohol. Water has a high heat capacity, which means that the water absorbs the energy from the flame and keep the bill from catching on fire. If you dipped the dollar bill in pure 100% alcohol, the temperature would rise high enough on the bill to burn. The reason we chose a bill instead of regular paper is that the dollar bill is a combination of linen and paper, making it much stronger and absorbent for this experiment.


You need both the water and the alcohol for this experiment. The water, as it absorbs the energy from the flame, heats up to its boiling point and then vaporizes, keeping the bill cool enough to not catch on fire. The alcohol is the fuel needed to keep the flame going. It’s a delicate balance between the two, but here are a couple of variations you can try out:


  • You can change the color of the flame by adding in a sprinkling of salt (for yellow), boric acid (for green), or epsom salt (for white).
  • You can also try mixing different ratios of water to alcohol, using 50%, 70% and 91% isopropyl alcohol. You can also try ethyl alcohol (which is an entirely different molecule) but will react about the same with this experiment. Note that if you decrease the water content too much, you’re going to lose your dollar bill.

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Click here to go to next lesson on Detonating Bubbles.


Combustion

Monday June 12, 2017

A combustion reaction gives off energy, usually in the form of heat and light.  The reaction itself includes oxygen combining with another compound to form water, carbon dioxide, and other products.


A campfire is an example of wood and oxygen combining to create ash, smoke, and other gases. Here’s the reaction for the burning of methane (CH4) which gives carbon dioxide (CO2) and water (H2O):
CH4 + 2 O2  CO2 + 2 H2O
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We will be creating hydrogen gas by making a heterogeneous mixture of zinc powder and calcium hydroxide and heat it. The hydrogen bubbles into test tube in a water bath. When we mix our test tube of hydrogen with the air the room, the hydrogen burns…it actually explodes. Our amounts are small, but you will witness a cool, small, explosion.


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Click here to go to next lesson on What is Fire?

Hess’s Law

Monday June 12, 2017

First Law of Thermodynamics: Energy is conserved. Energy is the ability to do work. Work is moving something against a force over a distance. Force is a push or a pull, like pulling a wagon or pushing a car. Energy cannot be created or destroyed, but can be transformed.


Materials: ball, string


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Roll a ball down a hill. The amount of energy the ball had while at rest at the top of the hill (potential energy) turns into kinetic energy while it zips to the bottom.


You can also swing on a swing and see this effect happen over and over again: when you’re at the highest point of your swing, you have the highest potential energy but zero kinetic energy (your speed momentarily goes to zero as you change direction). At the lowest point of your swing (when you’re moving the fastest), all your potential energy has turned into kinetic energy. Why do you eventually stop? The reason you eventually slow down and stop instead of swinging back and forth forever is that you have air resistance and friction where the chain is suspended from the bar.


Learn more about this scientific principle in Unit 4 and Unit 5 and Unit 13.
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Click here to go to next lesson on 1st law of thermodynamics.

More Endo & Exo Reactions

Monday June 12, 2017

By knowing the value of the bond energy, we can predict if a chemical reaction will be exothermic or endothermic. If the bonds in the products are stronger than the bonds in the reactants, then the products are more stable and the reaction will give off heat (exothermic).


Exothermic chemical reactions release energy as heat, light, electrical or sound (or all four). Usually when someone says it’s an exothermic reaction, they usually just mean energy is being released as heat.


Some release heat gradually (for example, a disposable hand-warmer), while others are more explosive (like burning magnesium). The energy comes from breaking the bonds within the chemical reaction.


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Other chemical reactions will just sit there and do nothing, unless you add energy to it first. These types of reactions need to absorb energy in order to react, so you’ll notice a temperature drop when the reaction takes place (a disposable ice pack, for example, is a chemical reaction that takes place using the energy from the water, so it makes the water colder when it uses this energy).


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Click here to go to next lesson on Hess’s Law.


Endothermic and Exothermic Reactions

Monday June 12, 2017

Dissolving calcium chloride is highly exothermic, meaning that it gives off a lot of heat when mixed with water (the water can reach up to 140oF, so watch your hands!). The energy released comes from the bond energy of the calcium chloride atoms, and is actually electromagnetic energy.


When you combine the calcium chloride and sodium carbonate solutions, you form the new chemicals sodium chloride (table salt) and calcium carbonate. Both of these new chemicals are solids and “fall out” of the solution, or precipitate. If you find that there is still liquid in the final solution, you didn’t have quite a saturation solution of one (or both) initial solutions.


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Materials:


  • calcium chloride (AKA: “ice melt” or “Dri-EZ”)
  • sodium carbonate (AKA: “washing soda”)
  • two disposable cups
  • two test tubes with caps
  • medicine dropper
  • distilled water
  • goggles and gloves


Download Student Worksheet & Exercises


Mix up a saturated solution of calcium chloride in one test tube and a saturated solution of sodium carbonate in the other. Here’s how to do this:


Sprinkle 1 teaspoon of calcium chloride into a disposable cup. Add in a few tablespoons of water and stir, dissolving as much of the solid into the water as possible. Add more calcium chloride until you see bits of it at the bottom that refuse to dissolve. Now pour only the liquid into your test tube; the liquid is your saturated solution. Do the same for the sodium carbonate.


Do the test tubes feel hot or cold? Pour one test tube into another.


Instant solid.


Calcium chloride is hygroscopic (absorbs moisture), exothermic (releases heat when melted or dissolved), and deliquescent (dissolves in the moisture it absorbs and retains it for a long time).


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Click here to go to next lesson on endo/exo reactions.

Law of conservation of energy, work, and internal energy

Monday June 12, 2017

This experiment is for advanced students. Did you know that eating a single peanut will power your brain for 30 minutes? The energy in a peanut also produces a large amount of energy when burned in a flame, which can be used to boil water and measure energy.


Peanuts are part of the bean family, and actually grows underground (not from trees like almonds or walnuts).  In addition to your lunchtime sandwich, peanuts are also used in woman’s cosmetics, certain plastics, paint dyes, and also when making nitroglycerin.


What makes up a peanut?  Inside you’ll find a lot of fats (most of them unsaturated) and  antioxidants (as much as found in berries).  And more than half of all the peanuts Americans eat are produced in Alabama. We’re going to learn how to release the energy inside a peanut and how to measure it.


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Materials:


  • raw peanuts
  • chemistry stand with glass test tube and holder (watch video)
  • flameproof surface (large ceramic tile or cookie sheet)
  • paper clip
  • alcohol burner or candle with adult help
  • fire extinguisher


Download Student Worksheet & Exercises


What’s Going On? There’s chemical energy stored inside a peanut, which gets transformed into heat energy when you ignite it. This heat flows to raise the water temperature, which you can measure with a thermometer.  You should find that your peanut contains 1500-2100 calories of energy!  Now don’t panic…  this isn’t the same as the number of calories you’re allowed to eat in a day.  The average person aims to eat around 2,000 Calories (with a capital “C”).  1 Calorie = 1,000 calories.  So each peanut contains 1.5-2.1 Calories of energy (the kind you eat in a day). Do you see the difference?


But wait… did all the energy from the peanut go straight to the water, or did it leak somewhere else, too?  The heat actually warmed up the nearby air, too, but we weren’t able to measure that. If you were a food scientist, you’d use a nifty little device known as a bomb calorimeter to measure calorie content.  It’s basically a well-insulated, well-sealed device that catches nearly all the energy and flows it to the water, so you get a much more accurate temperature reading. (Using a bomb calorimeter, you’d get 6.1-6.8 Calories of energy from one peanut!)


How do you calculate the calories from a peanut?

Let’s take an example measurement.  Suppose you measured a temperature increase from 20 °C to 100 °C for 10 grams of water, and boiled off 2 grams.  We need to break this problem down into two parts – the first part deals with the temperature increase, and the second deals with the water escaping as vapor.


The first basic heat equation is this:


Q = m c T


Q is the heat flow (in calories)
m is the mass of the water (in grams)
c is the specific heat of water (which is 1 degree per calorie per gram)
and T is the temperature change (in degrees)


So our equation becomes: Q = 10 * 1 * 80 = 800 calories.


If you measured that we boiled off 2 grams of water, your equation would look like this for heat energy:


Q = L m


L is the latent heat of vaporization of water (L= 540 calories per gram)
m is the mass of the water (in grams)


So our equation becomes: Q = 540 * 2 = 1080 calories.


The total energy needed is the sum of these two:


Q = 800 calories + 1080 calories = 1880 calories.


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Click here to go to next lesson on Endothermic and exothermic reactions.

Energy from a peanut

Monday June 12, 2017

This experiment is for advanced students. Did you know that eating a single peanut will power your brain for 30 minutes? The energy in a peanut also produces a large amount of energy when burned in a flame, which can be used to boil water and measure energy.


Peanuts are part of the bean family, and actually grows underground (not from trees like almonds or walnuts).  In addition to your lunchtime sandwich, peanuts are also used in woman’s cosmetics, certain plastics, paint dyes, and also when making nitroglycerin.


What makes up a peanut?  Inside you’ll find a lot of fats (most of them unsaturated) and  antioxidants (as much as found in berries).  And more than half of all the peanuts Americans eat are produced in Alabama. We’re going to learn how to release the energy inside a peanut and how to measure it.


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Materials:


  • raw peanuts
  • chemistry stand with glass test tube and holder (watch video)
  • flameproof surface (large ceramic tile or cookie sheet)
  • paper clip
  • alcohol burner or candle with adult help
  • fire extinguisher


Download Student Worksheet & Exercises


What’s Going On? There’s chemical energy stored inside a peanut, which gets transformed into heat energy when you ignite it. This heat flows to raise the water temperature, which you can measure with a thermometer.  You should find that your peanut contains 1500-2100 calories of energy!  Now don’t panic…  this isn’t the same as the number of calories you’re allowed to eat in a day.  The average person aims to eat around 2,000 Calories (with a capital “C”).  1 Calorie = 1,000 calories.  So each peanut contains 1.5-2.1 Calories of energy (the kind you eat in a day). Do you see the difference?


But wait… did all the energy from the peanut go straight to the water, or did it leak somewhere else, too?  The heat actually warmed up the nearby air, too, but we weren’t able to measure that. If you were a food scientist, you’d use a nifty little device known as a bomb calorimeter to measure calorie content.  It’s basically a well-insulated, well-sealed device that catches nearly all the energy and flows it to the water, so you get a much more accurate temperature reading. (Using a bomb calorimeter, you’d get 6.1-6.8 Calories of energy from one peanut!)


How do you calculate the calories from a peanut?

Let’s take an example measurement.  Suppose you measured a temperature increase from 20 °C to 100 °C for 10 grams of water, and boiled off 2 grams.  We need to break this problem down into two parts – the first part deals with the temperature increase, and the second deals with the water escaping as vapor.


The first basic heat equation is this:


Q = m c T


Q is the heat flow (in calories)
m is the mass of the water (in grams)
c is the specific heat of water (which is 1 degree per calorie per gram)
and T is the temperature change (in degrees)


So our equation becomes: Q = 10 * 1 * 80 = 800 calories.


If you measured that we boiled off 2 grams of water, your equation would look like this for heat energy:


Q = L m


L is the latent heat of vaporization of water (L= 540 calories per gram)
m is the mass of the water (in grams)


So our equation becomes: Q = 540 * 2 = 1080 calories.


The total energy needed is the sum of these two:


Q = 800 calories + 1080 calories = 1880 calories.


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Click here to go to next lesson on Law of conservation of energy, work, and internal energy.


Heat Capacity and Specific Heat

Monday June 12, 2017

Do you remember when I said that heat and temperature are two different things? Heat is energy – it is thermal energy. It can be transferred from one object to another.


Here’s what you do:


  • Find your balloon.
  • Put the balloon under the faucet and fill the balloon with a couple of tablespoons of water. Not too much!
  • Now blow up the balloon and tie it, leaving the water in the balloon.
  • You should have an inflated balloon with a tablespoon or two of water at the bottom of it.
  • Have your adult helper carefully light the candle. Don’t do this next to your computer… do it in the sink.
  • Hold the balloon over the candle carefully for a couple of seconds.
  • Did it pop?

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Water is very good at absorbing heat without increasing in temperature which is why it is used in car radiators and nuclear power plants. Whenever someone wants to keep something from getting too hot, they will often use water to absorb the heat.


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Click here to go to next lesson on Fire Balloon.

Fire Balloon

Monday June 12, 2017

If you’ve ever had a shot, you know how cold your arm feels when the nurse swipes it with a pad of alcohol. What happened there? Well, alcohol is a liquid with a fairly low boiling point. In other words, it goes from liquid to gas at a fairly low temperature. The heat from your body is more then enough to make the alcohol evaporate.


As the alcohol went from liquid to gas it sucked heat out of your body. For things to evaporate, they must suck in heat from their surroundings to change state. As the alcohol evaporated you felt cold where the alcohol was. This is because the alcohol was sucking the heat energy out of that part of your body (heat was being transferred by conduction) and causing that part of your body to decrease in temperature.


As things condense (go from gas to liquid state) the opposite happens. Things release heat as they change to a liquid state. The water gas that condenses on your mirror actually increases the temperature of that mirror. This is why steam can be quite dangerous. Not only is it hot to begin with, but if it condenses on your skin it releases even more heat which can give you severe burns. Objects absorb heat when they melt and evaporate/boil. Objects release heat when they freeze and condense.


Do you remember when I said that heat and temperature are two different things? Heat is energy – it is thermal energy. It can be transferred from one object to another by conduction, convection, and radiation. We’re now going to explore heat capacity and specific heat. Here’s what you do:


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You Need:


  • Balloon
  • Water
  • Matches, candle, and adult help
  • Sink


Download Student Worksheet & Exercises


1. Put the balloon under the faucet and fill the balloon with some water.


2. Now blow up the balloon and tie it, leaving the water in the balloon. You should have an inflated balloon with a tablespoon or two of water at the bottom of it.


3. Carefully light the match or candle and hold it under the part of the balloon where there is water.


4. Feel free to hold it there for a couple of seconds. You might want to do this over a sink or outside just in case!


So why didn’t the balloon pop? The water absorbed the heat! The water actually absorbed the heat coming from the match so that the rubber of the balloon couldn’t heat up enough to melt and pop the balloon. Water is very good at absorbing heat without increasing in temperature which is why it is used in car radiators and nuclear power plants. Whenever someone wants to keep something from getting too hot, they will often use water to absorb the heat.


Think of a dry sponge. Now imagine putting that sponge under a slowly running faucet. The sponge would continue to fill with water until it reached a certain point and then water started to drip from it. You could say that the sponge had a water capacity. It could hold so much water before it couldn’t hold any more and the water started dripping out. Heat capacity is similar. Heat capacity is how much heat an object can absorb before it increases in temperature. This is also referred to as specific heat. Specific heat is how much heat energy a mass of a material must absorb before it increases 1°C.


Exercises Answer the questions below:


  1. What is specific heat?
    1. The specific amount of heat any object can hold
    2. The amount of energy required to raise the temperature of an object by 1 degree Celsius.
    3. The type of heat energy an object emits
    4. The speed of a compound’s molecules at room temperature
  2. Name two types of heat energy:
  3. What type (or types) of heat energy is at work in today’s experiment?
  4. True or False: Water is poor at absorbing heat energy.
    1. True
    2. False

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Click here to go to next lesson on Energy from a peanut.


Ice Cream

Monday June 12, 2017

Is it hot where you live in the summer? What if I gave you a recipe for making ice cream that doesn’t require an expensive ice cream maker, hours of churning, and can be made to any flavor you can dream up? (Even dairy-free if needed?)


If you’ve got a backyard full of busy kids that seem to constantly be in motion, then this is the project for you.  The best part is, you don’t have to do any of the churning work… the kids will handle it all for you!


This experiment is simple to set up (it only requires a trip to the grocery store), quick to implement, and all you need to do guard the back door armed with a hose to douse the kids before they tramp back into the house afterward.


One of the secrets to making great ice cream quickly is [am4show have=’p8;p9;p23;p50;p80;p88;p101;’ guest_error=’Guest error message’ user_error=’User error message’ ] to be sure that the milk and cream is COLD.  I will make this particular recipe, it’s usually with hundreds of kids, and our staff will stuff the milk products in the freezer for an hour or two or under hundreds of pounds of ice to make sure it’s super-cold.


If you’re going for the dairy-free kind, simply skip the milk and cream and add a bit of extra time to the chill time of your substitute ‘milk’.  We’ve had the best luck with almond and soy milk. Are you ready?


Here’s what you need:


Materials:


  • 1 quart whole milk (do not substitute, unless your child has a milk allergy, then use soy or almond milk)
  • 1 pint heavy cream (do not substitute, unless your child has a milk allergy, then skip)
  • 1 cup sugar (or other sweetener)
  • 1 tsp vanilla (use non-alcohol kind)
  • rock salt (use table salt if you can’t find it)
  • lots of ice
  • freezer-grade zipper-style bags (you’ll need quart and gallon sizes)


Download Student Worksheet & Exercises


How does that work? Ice cream is basically “fluffy milk”. You need to whip in a lot of air into the milk fat to get the fluffy pockets that make this stuff worthwhile. The more the kids shake the bag, the faster it will turn into ice cream.


Why do we put salt on the ice?


If you live in an area where they put salt on the roads, you already know that people do this to melt the ice. But how does salt melt ice? Think about the chemistry of what’s going on. Water normally freezes at zero degrees Celsius. But salt water presses lower than zero, so the freezing point of salt water is lower than fresh water. By sprinkling salt on the roads, you’re lowering the point at which water freezes at. When you add a solute (salt) to the solvent (water) to alter the freezing point of the solution, it’s known as the “freezing point depression”.


Tips: Don’t use nonfat milk – it won’t work with this style of ice-cream making.  if you’re adding fruit or chocolate bits, make sure you get those cold in advance too, or they will slow down your process as they heat your milk solution. (We usually add those bits last after the ice cream is done.)


IMPORTANT: Do NOT substitute dry ice for the water ice – the carbon dioxide gases build quickly and explode the bag, and now you have flying bits of dry ice that will burn skin upon contact.  That’s not the biggest issue, though… the real problem is that now animals (like your dog) and small children pop a random piece of dry ice into their mouths, which will earn your family a visit to the ER. So stick with the regular ice from your fridge.


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Click here to go to next lesson on Heat Capacity and Specific Heat.


Energy, Enthalpy, and Hess’s Law

Sunday June 11, 2017

You can think of enthalpy as the total potential energy of a system given by this equation:


ΔH = ΔU + Δ(pV)  (U = internal energy, p = pressure, V = volume)


Since for most experiments, pressure is constant, that equation becomes:


ΔH = ΔU + pΔV


The heat transfer of a system is given by q and it can be positive or negative. A hot cup of coffee on a cold morning is warmer than its environment, so heat will flow from the coffee to the cooler surrounding air, since heat always flows from hot to cold, so q is negative. If you have ice-cold lemonade on a hot day, heat flows from the environment to the lemonade, so q is positive. The mathematical equation for heat is:


q = ΔU − W  (W = work)


When you combine the equations to find the relationship between heat and enthalpy, you find that:


ΔH = q  when pressure is constant. Now let’s learn how to use this equation in chemistry to find the energy in a chemical reaction.


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Thermal Energy

Saturday June 10, 2017

Thermal energy is how much the molecules are moving inside an object. The faster molecules move, the more thermal energy it has.


Objects whose molecules are moving very quickly are said to have high thermal energy or high temperature. Like a cloud of steam, for example. The higher the temperature, the faster the molecules are moving.
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Remember that temperature is just a speedometer for molecules. The speed of the molecules in ice cream is way slower than it is in a hot shower.


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Click here to go to next lesson on Make ice cream.

Thermometer

Saturday June 10, 2017

First invented in the 1600s, thermometers measure temperature using a sensor (the bulb tip) and a scale. Temperature is a way of talking about, measuring, and comparing the thermal energy of objects. We use three different kinds of scales to measure temperature. Fahrenheit, Celsius, and Kelvin. (The fourth, Rankine, which is the absolute scale for Fahrenheit, is the one you’ll learn about in college.)


Mr. Fahrenheit, way back when (18th century) created a scale using a mercury thermometer to measure temperature. He marked 0° as the temperature ice melts in a tub of salt. (Ice melts at lower temperatures when it sits in salt. This is why we salt our driveways to get rid of ice). To standardize the higher point of his scale, he used the body temperature of his wife, 96°.


As you can tell, this wasn’t the most precise or useful measuring device. I can just imagine Mr. Fahrenheit, “Hmmm, something cold…something cold. I got it! Ice in salt. Good, okay there’s zero, excellent. Now, for something hot. Ummm, my wife! She always feels warm. Perfect, 96°. ” I hope he never tried to make a thermometer when she had a fever.


Just kidding, I’m sure he was very precise and careful, but it does seem kind of weird. Over time, the scale was made more precise and today body temperature is usually around 98.6°F.


Later, (still 18th century) Mr. Celsius came along and created his scale. He decided that he was going to use water as his standard. He chose the temperature that water freezes at as his 0° mark. He chose the temperature that water boils at as his 100° mark. From there, he put in 100 evenly spaced lines and a thermometer was born.


Last but not least Mr. Kelvin came along and wanted to create another scale. He said, I want my zero to be ZERO! So he chose absolute zero to be the zero on his scale.


Absolute zero is the theoretical temperature where molecules and atoms stop moving. They do not vibrate, jiggle or anything at absolute zero. In Celsius, absolute zero is -273 ° C. In Fahrenheit, absolute zero is -459°F (or 0°R). It doesn’t get colder than that!


As you can see, creating the temperature scales was really rather arbitrary:


“I think 0° is when water freezes with salt.”
“I think it’s just when water freezes.”
“Oh, yea, well I think it’s when atoms stop!”


Many of our measuring systems started rather arbitrarily and then, due to standardization over time, became the systems we use today. So that’s how temperature is measured, but what is temperature measuring?


Temperature is measuring thermal energy which is how fast the molecules in something are vibrating and moving. The higher the temperature something has, the faster the molecules are moving. Water at 34°F has molecules moving much more slowly than water at 150°F. Temperature is really a molecular speedometer.


Let’s make a quick thermometer so you can see how a thermometer actually works:


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Materials:


  • plastic bottle
  • straw
  • hot glue or clay
  • water
  • food coloring
  • rubbing alcohol
  • index card and pen


When something feels hot to you, the molecules in that something are moving very fast. When something feels cool to you, the molecules in that object aren’t moving quite so fast. Believe it or not, your body perceives how fast molecules are moving by how hot or cold something feels. Your body has a variety of antennae to detect energy. Your eyes perceive certain frequencies of electromagnetic waves as light. Your ears perceive certain frequencies of longitudinal waves as sound. Your skin, mouth and tongue can perceive thermal energy as hot or cold. What a magnificent energy sensing instrument you are!


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Click here to go to next lesson on Thermal Energy.

Introduction to Thermochemistry

Saturday June 10, 2017

Energy is the capacity to do work or to transfer heat. You do work when you walk up a flight of stairs. You can feel the heat from the sun when you step in the sunlight. Both are energy.


Heat is associated with changing the temperature of an object. The temperature changes because energy is being transferred to it. Another word for heat is thermal energy.


Thermochemistry is the science of heat or thermal energy transfer and how to use it with chemical reactions.
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Click here to go to next lesson on Thermometer Here.

Titrations and pH curves

Friday June 9, 2017

What do you do if you don’t know the concentration of a solution? We use a method called titration to determine how many moles are present in the solution of an acid or a base by neutralizing it. A titration curve is when you graph out the pH as you drop it in the solution.


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Chemical Bonds

Friday June 9, 2017

Now let’s take a look at the forces between the molecules themselves. There are four main interactions which really come down to different ways of having opposite charges attract each other.


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Periodic Table Arrangement & Electron Configuration

Wednesday June 7, 2017

The periodic table is more like a filing cabinet that tells you everything about the structure of the atom, its properties and how it behave in chemical reactions. With just a quick glance, you will soon be able to tell how the electrons are organized around the nucleus and also predict how the atom will interact with others.


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Ionization Energy

Wednesday June 7, 2017

Ionization energy is the energy needed to remove electrons from an atom.


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Quantum Model of the Atom

Wednesday June 7, 2017

The Bohr model is useful when we want to tell how reactive an element is, but it doesn’t really work to explain how the electrons are organized around the nucleus. The quantum model is the one used today by scientists.


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Photons and Energy

Wednesday June 7, 2017
Light is energy that can travel through space. How much energy light has determines what kind of wave it is – visible, x-ray, radio, microwave… . The electromagnetic spectrum shows the different energies of light and how the energy relates to different frequencies.

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Click here to go to next lesson on Photoelectric Effect.


Valence Electrons

Wednesday June 7, 2017

The number of electrons in the outermost shell tells you how reactive the atom is because it tells you how many it needs to feel full, or how many it can lose. Valence electrons are the highest energy and furthest out electrons. In general, elements are less reactive when their outermost shell is full.


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Condensing Steam

Wednesday June 7, 2017

An average can of soda at room temperature measures 55 psi before you ever crack it open. (In comparison, most car tires run on 35 psi, so that gives you an idea how much pressure there is inside the can!)


If you heat a can of soda, you’ll run the pressure over 80 psi before the can ruptures, soaking the interior of your house with its sugary contents. Still, you will have learned something worthwhile: adding energy (heat) to a system (can of soda) causes a pressure increase. It also causes a volume increase (kaboom!).
How about trying a safer variation of this experiment using water, an open can, and implosion instead of explosion?


Materials – An empty soda can, water, a pan, a bowl, tongs, and a grown-up assistant.


NOTE: If you can get a hold of one, use a beer can – they tend to work better for this experiment. But you can also do this with a regular old soda can. And no, I am not suggesting that kids should be drinking alcohol! Go ask a parent to find you one – and check the recycling bin.


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Prepare an ice bath by putting about ½” of ice water in a shallow dish. With an adult, place a few tablespoons of water in an empty soda or beer can and place the can upright in a skillet on the stove. When the can emits a think trickle of steam, grab the can with tongs and quickly invert it into the ice dish. CRACK!


Troubleshooting: The trick to making this work is that the can needs to be full of hot steam, which is why you only want to use a tablespoon or two of water in the bottom of the can. It’s alright if a bit of water is still at the bottom of the can when you flip it into the ice bath. In fact, there should be some water remaining or you’ll superheat the steam and eventually melt the can. You want enough water in the ice bath to completely submerge the top of the can.


Always use tongs when handling the heated can and make sure you completely submerge the top of the can in the icy water. The water needs to seal the hole in the top of the can so the steam doesn’t escape. Be prepared for a good, loud CRACK! when you get it right.


Why does this work? By heating up the water in the can, you’re changing the state of water from a liquid to a has (called water vapor), which drives out the air, leaving the steam inside. When inverted and cooled, the steam condenses to a small volume of liquid water (much smaller than if it was just hot air). The molecules in water vapor are a lot further apart than when they are in a liquid state. Since the air inside the can has been replaced by the steam, when it cools quickly, it creates a lower air pressure region in the can, so the air pressure surrounding the outside of the can rapidly crushes the can.


If you look really carefully as it condenses, you’ll see cold water from the bowl zoom into the can, just like when you suck water through a straw. The vacuum created int he can by the condensing steam creates a lower pressure, which pushes water into the can itself. When you suck from a straw, you’re creating a lower air pressure region in your mouth so that the surrounding air pressure pushes liquid up the straw to equalize the pressure.


Remember, high pressure always pushes!


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Click here for Homework Problem Set #4


Generating Oxygen

Wednesday June 7, 2017

This experiment is for advanced students.


This time we’re going to use a lot of equipment… really break out all the chemistry stuff. We’ll need all this stuff to generate oxygen with potassium permanganate (KMNO4). We will work with this toxic chemical and we will be careful…won’t we?


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Oxygen is pretty important… it’s only the single most important thing that mammals need. Besides breathing, oxygen is important for so much on this world. Oxygen is used in welding, rocket fuel, and water treatment. Without oxygen, there is no oxidation and no fire. Simply put, we wouldn’t have rusty bicycles or campfires. Can your believe it?


Potassium permanganate is an important chemical in the film industry. It is used to make props like cloth, ropes, and glass, appear “old”. Some films it has been used in are “Troy”, “Indiana Jones”, and “300”. The KMnO4 stains any organic material. KMnO4 is also used as an antiseptic, and is used to treat skin ulcers and rashes. It is also used to treat foot fungus…..phew! People living in the country are sometimes plagued with an iron taste or a rotten egg smell in the water from their wells. Potassium permanganate can be used to remove the taste and smell from the water.


Materials:


  • Chemistry stand
  • Plastic tub
  • Water
  • 2 test tubes
  • Test tube clamp
  • Potassium permanganate (KMnO4) (MSDS)
  • Alcohol burner
  • Lighter
  • One-hole rubber stopper
  • Solid rubber stopper
  • 900 bend glass tube
  • Measuring spoon
  • Rubber tubing
  • Match
  • Wooden splint

Be careful inserting the glass tubing into the stopper. Wet the short end of the glass tube with water and gently push and twist the glass through the stopper. Wear work gloves and work carefully and slowly. Do not use oil or grease you have laying around the house.


When lighting the oxygen in the test tube, use a wooden splint. Wooden splints can be purchased from craft stores, or make your own by shaving thin strips from a piece of pine wood.


C3000: Experiment 58


Download Student Worksheet & Exercises


Here’s what’s going on in this experiment:


2KMnO4 + O2 –> K2MnO4 + MnO2 + O2


Potassium permanganate is heated and produces potassium manganate, manganese dioxide, and oxygen


Oxygen is generated by heating the KMnO4, and is collected in the test tubes. We will test the contents of the tubes to see if oxygen has been generated. What do you think will happen when a glowing splint is pushed up inside the test tube? Don’t know? Do the experiment and try to figure it out. Remember, in order for there to be flame, you need fuel and oxygen. If that gas was carbon dioxide, what would happen when the glowing splint was placed inside?


Cleanup: Clean everything thoroughly after you are finished with the lab. After cleaning with soap and water, rinse thoroughly. Chemists use the rule of “three” in cleaning glassware and tools. After washing, chemists rinse out all visible soap and then rinse three times more.


Storage: Place all chemicals, cleaned tools, and glassware in their respective storage places.


Disposal: Dispose of all solid waste in the garbage. Liquids can be washed down the drain with running water. Let the water run awhile to ensure that they have been diluted and sent downstream.


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Click here to go to next lesson on condensing steam.


Pop Rockets

Wednesday June 7, 2017

Rockets shoot skyward with massive amounts of thrust, produced by chemical reaction or air pressure. Scientists create the thrust force by shoving a lot of gas (either air itself, or the gas left over from the combustion of a propellant) out small exit nozzles.


According to the universal laws of motion, for every action, there is equal and opposite reaction. If flames shoot out of the rocket downwards, the rocket itself will soar upwards. It’s the same thing if you blow up a balloon and let it go—the air inside the balloon goes to the left, and the balloon zips off to the right (at least, initially, until the balloon neck turns into a thrust-vectored nozzle, but don’t be concerned about that just now).


A rocket has a few parts different from an airplane. One of the main differences is the absence of wings. Rockets utilize fins, which help steer the rocket, while airplanes use wings to generate lift. Rocket fins are more like the rudder of an airplane than the wings.


Another difference is the how rockets get their speed. Airplanes generate thrust from a rotating blade, whereas rockets get their movement by squeezing down a high-energy gaseous flow and squeezing it out a tiny exit hole.


If you’ve ever used a garden hose, you already know how to make the water stream out faster by placing your thumb over the end of the hose. You’re decreasing the amount of area the water has to exit the hose, but there’s still the same amount of water flowing out, so the water compensates by increasing its velocity. This is the secret to converging rocket nozzles—squeeze the flow down and out a small exit hole to increase velocity.


There comes a point, however, when you can’t get any more speed out of the gas, no matter how much you squeeze it down. This is called “choking” the flow. When you get to this point, the gas is traveling at the speed of sound (around 700 mph, or Mach 1). Scientists found that if they gradually un-squeeze the flow in this choked state, the flow speed actually continues to increase. This is how we get rockets to move at supersonic speeds or above Mach 1.


f18The image shown here is a real picture of an aircraft as it breaks the sound barrier. This aircraft is passing the speed at which sounds travel. The white cloud you see in the photo is related to the shock waves that are forming around the craft as it moves into supersonic speeds. Because the aircraft is moving through air, which is a gas, the gas can compress and results in a shock wave.


You can think of a shock wave as big pressure front. In this photo, the pressure is condensing water vapor in the air, hence the cloud. There are lots of things on earth that break the sound barrier – bullets and bullwhips, for example. The loud crack from a whip is the tip zipping faster than the speed of sound.


The rockets we’re about to build get their thrust by generating enough pressure and releasing that pressure very quickly. You will generate pressure both by pumping and by chemical reaction, which generates gaseous products. Let’s get started!


For this experiment, you will need:


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  • film canister or other plastic container with a tight-fitting lid (like a mini-M&M container)
  • alka-seltzer or generic effervescent tablets
  • water
  • outside area for launching

The record for these rockets is 28′ high. What do you think about that? Note – you can use anything that uses a chemical reaction… what about baking soda and vinegar? Baking powder? Lemon juice?



Important question: Does more water, tablets, or air space give you a higher flight?


Variations: Add foam fins and a foam nose (try a hobby or craft shop), hot glued into place. Foam doesn’t mind getting wet, but paper does. Put the fins on at an angle and watch the seltzer rocket spin as it flies skyward. You can also tip the rocket on its side and add wheels for a rocket car, stack rockets, for a multi-staging project, or strap three rockets together with tape and launch them at the same time! You can also try different containers using corks instead of lids.



More Variations: What other chemicals do you have around that also produces a gas during the chemical reaction? Chalk and vinegar, baking soda, baking powder, hydrogen peroxide, isopropyl alcohol, lemon juice, orange juice, and so on.


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Advanced students: Download your Pop Rockets Lab here.


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Click here to go to next lesson on generating oxygen.

Rubber Eggs

Wednesday June 7, 2017

If you soak chicken bones in acetic acid (distilled vinegar), you’ll get rubbery bones that are soft and pliable as the vinegar reacts with the calcium in the bones. This happens with older folks when they lose more calcium than they can replace in their bones, and the bones become brittle and easier to break. Scientists have discovered calcium is replaced more quickly in bodies that exercise and eating calcium rich foods, like green vegetables.


This is actually two experiments in one – here’s what you need to do:


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Materials:


  • hard boiled egg
  • glass or clean jar
  • distilled white vinegar


Download Student Worksheet & Exercises


When you first plop the egg in the vinegar, do you notice the tiny bubbles? The acetic acid (distilled vinegar) reacts with the calcium carbonate in the eggshell, and you may even notice a color change over a couple of days.


How high does your egg bounce? Does it matter how long you leave it in the vinegar for?


The second part of this experiment is to try this again, but now use a raw egg (wash your hands after handling your egg due to salmonella!) You’ll get a difference result – the eggshell will become flexible, but don’t bounce them.


Exercises


  1. Describe what the eggshell looked like before the reaction.
  2. Describe the acetic acid
  3. The product you witnessed in this chemical reaction was carbon dioxide, a colorless, odorless gas. How can you tell there really was a chemical reaction?
  4. Why did the egg turn to “rubber?”

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Click here to go to next lesson on Pop Rockets.


Gas Forming Reactions

Wednesday June 7, 2017

Gas forming reactions are also exchange reactions. The best example I can think of for this type of reaction is what happens when you put a piece of chalk in a cup of vinegar. The chalk, which is mostly CaCO3 (calcium carbonate) and vinegar (acetic acid) forms calcium chloride and carbonic acid, which isn’t stable and quickly turns into water and carbon dioxide. A faster version of this experiment is what happens when you take an effervescent tablet, like alka seltzer, and stick it in water, because the tablet is actually a solid form of baking soda and vinegar put together. What happens when you mix baking soda and vinegar together?


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Lots of bubbles! Baking soda and vinegar is a gas forming exchange reaction.


There’s actually two reactions going – the first one is a double displacement where the vinegar reactions with the backing soda to make sodium acetate and carbonic acid, but the carbonic acid is unstable and breaks into carbon dioxide and water. The bubbles you see from this reaction are the carbon dioxide bubbles escaping., Since CO2 is heavier than air, it sits on the surface or overflows off the side of the container. If you add soap to this reaction, you’ll see the bubbles more clearly. If you warm up the vinegar first, the reaction will happen faster. The white sludge at the bottom os sodium acetate that’s left ver. Adults use this in making rubber tires, for curing headaches… that sort of thing.


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Click here to go to next lesson on Rubber Eggs.

Real Gases And Deviation From Ideal Gas Law

Wednesday June 7, 2017

The kinetic theory of gases assumes that all gases behave ideally, but we know that’s not really what happens in the real world. For example, real gas particles do occupy space and also attract each other, although these properties are more apparent at lower temperature because usually the particles have enough kinetic energy to zip by each other without worrying about the attractive or repulsive charges from other molecules. If the molecules move slow enough though, they do get affected by the push or pull of other molecules.


Also at high pressures, the molecules are so tightly packed together that they do start to have volume considerations that need to be addressed. So for a real gas, we can make calculations like this:


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Click here to go to next lesson on Gas Forming Reactions.

Can Fish Drown?

Wednesday June 7, 2017

If you’ve ever owned a fish tank, you know that you need a filter with a pump. Other than cleaning out the fish poop, why else do you need a filter? (Hint: think about a glass of water next to your bed. Does it taste different the next day?)


There are tiny air bubbles trapped inside the water, and you can see this when you boil a pot of water on the stove. The experimental setup shown in the video illustrates how a completely sealed tube of water can be heated… and then bubbles come out one end BEFORE the water reaches a boiling point. The tiny bubbles smoosh together to form a larger bubble, showing you that air is dissolved in the water.


Materials:


  • test tube clamp
  • test tube
  • lighter (with adult help)
  • alcohol burner or votive candle
  • right-angle glass tube inserted into a single-hole stopper
  • regular tap water

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Download Student Worksheet & Exercises


The filter pump in your fish tank ‘aerates’ the water. The simple act of letting water dribble like a waterfall is usually enough to mix air back in. Which is why flowing rivers and streams are popular with fish – all that fresh air getting mixed in must feel good! The constant movement of the river replaces any air lost and the fish stay happy (and breathing). Does it make sense that fish can’t live in stagnant or boiled water?


You don’t need the fancy equipment show in this video to do this experiment… it just looks a lot cooler. You can do this experiment with a pot of water on your stove and watch for the tiny bubbles before the water reaches 212oF.


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Click here to go to next lesson on Real Gases And Deviation From Ideal Gas Law.


Temperature Effects On Gas Solubility

Wednesday June 7, 2017

We’re going to do an experiment where it will look like we can boil soda on command… but the truth is, it’s not really boiling in the first place! If you drink soda, save one for doing this experiment. Otherwise, get one that’s “diet” (without the sugar, it’s a lot easier to clean up).


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Materials:


  • two beakers or two saucepans
  • test tube
  • test tube clamp
  • stove or alcohol burner with stand
  • ice
  • soda (cold!)
  • gloves
  • goggles


Advanced Students: Download your Worksheet Lab here!


Experiment:


  1. Use the saucepan to heat a jar full of water until boiling (be sure to put an inch of water in the pan also or you’ll crack the jar).
  2. Fill one of the beakers with mostly ice and a little water. This is your ice bath.
  3. Fill your test tube half full with soda, and set it in the beaker with the hot water. What happens?
  4. Use the test tube clamp to remove the test tube from the hot water and place it in the ice bath. What happens now after you wait a few minutes?
  5. After a bit, place the test tube back into the hot water. What happens after a few minutes?
  6. Repeat this process and notice how and when the soda bubbles, and when it doesn’t. What do you think is happening?

What’s going on? The boiling point of the soda is much higher than the boiling point of water (due to the sugar added to the solution), however it sure looks like it is boiling, doesn’t it? Soda (a liquid solvent) has carbon dioxide gas (a gaseous solute) dissolved in it. When you heat it up, the increase in temperature makes the carbon dioxide comes out of the solution. Lowering the temperature makes the gas dissolve into the liquid, because the solubility of the soda is increased (how much gas you can dissolve into the solution). Gases are less soluble in hot solvents than cold, which is the opposite for solid solutes. Said another way, you can dissolve more salt in hot water than cold, and dissolve more gas bubbles in cold water than hot.
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Click here to go to next lesson on Can Fish Drown?.

Kinetic Molecular Theory

Wednesday June 7, 2017

The kinetic theory of gases relates what’s going on with the motion of the tiny invisible molecules with the properties you can measure, like temperature and pressure. Kinetic means the study of motion, and for us, it’s the motion of the gas molecules.


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Click here to go to next lesson on Temperature Effects On Gas Solubility.

Mean Free Path

Wednesday June 7, 2017

The “mean free path” is the average distance a gas molecule travels between collisions. If a molecule has a diameter “d”, then the effective cross section for a collision is “π d2“. This is used mostly with the Kinetic Theory of Gases, and is a good estimation of how particles move in a gas.
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Also useful when describing the motions of the molecules in a gas (again using the Kinetic Molecular Theory) is the average velocity of the molecules. Since the gas molecules are constantly moving about, it would be ridiculously hard to individually account for each molecule’s individual speed and direction at any given time. Instead, we make use of statistics to get an overall average estimate of the motion of the particles using the “root mean square” technique applied to gases.


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Click here to go to next lesson on Kinetic Molecular Theory.


Graham’s Law

Wednesday June 7, 2017

Graham’s law tells is how gases move through porous materials, like air in a balloon. Ever noticed how balloons don’t stay inflated forever? That’s because the gas diffuses through the balloon skin itself. And if you take a good look, helium balloons deflate the next day, whereas normal air balloons will keep for a few days. Small helium molecules effuse through the tiny holes in the balloon skin much faster than normal air does.
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Click here to go to next lesson on Mean Free Path.

Molar volume of gases and Avogadro’s Law

Wednesday June 7, 2017

Avogadro’s Law states that 1 mole of every gas occupies the same volume at the same temperature and pressure. The mass of the gas might be different… one mole of helium is going to weigh less than one mole of nitrogen, for example, but the number of helium gas molecules is exactly the same as the number of nitrogen molecules, and both of them will occupy the same amount of space (22.4L) at standard temperature and pressure. At room temperature and pressure, it’s slightly higher (24 L).
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Click here to go to next lesson on Graham’s Law.

Ideal Gas Law

Wednesday June 7, 2017

Okay, so now I want you to imagine a room full of ping pong balls that can bounce all by themselves. They go zipping all over the place all on their own. Now take those ping pong balls and add energy to them so now they bounce twice as fast. Got it?


Now what happens if we take away energy from them? Do they bounce slower? Yup!


Okay, now get them back to their original bouncing speed. Now take the room and make it smaller, like half it’s size, but keep the ping pong ball speed the same. Do they hit the walls more or less frequently? More! Are they speeding up or slowing down? Speeding up!


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Now take the room and expand it ten times it’s normal size. Do the balls hit the walls more or less now? Less! Do they still have the same speed? No, they should be slowing down, too.


So those ping pong balls are molecules, and when you add energy, you’re increasing the temperature so they fly around faster. When you increase the temperature, the molecules zip around faster and faster.


Dalton’s Law of partial pressures is related to the Ideal Gas law. Dalton’s Law states that in a mixture of non-reacting gases, like air, for example, the total pressure exerted is the sum of the partial pressures of each of the individual pressures. For air, you would simply sum up all the partial pressures of each of the individual gases of oxygen, nitrogen, argon, carbon dioxide, and water vapor to get the total air pressure.


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Click here to go to next lesson on Overview of the Ideal Gas Law.

Overview of the Ideal Gas Law

Wednesday June 7, 2017

Pure substances all behave about the same when they are gases. The Ideal Gas Law relates temperature, pressure, and volume of these gases in one simple statement: PV = nRT where P = pressure, V = volume, T = temperature, n = number of moles, and R is a constant.


When temperature increases, pressure and volume increase. Temperature is basically a speedometer for molecules. The faster they are wiggling and jiggling, the higher the temperature and the higher the thermal energy that object has. Pressure is how many pushes a surface feels from the motion of the molecules.


Materials: balloon, freezer, tape measure (optional)


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Hold a balloon in your hands and try to stuff it into a cup. Why is this so hard? You’re decreasing the volume and therefore increasing the pressure inside the balloon. (Since a balloon is so stretchy, this is near impossible to do without laughing.) You are compressing the balloon and thus increasing both the pressure and temperature inside the balloon slightly.


Blow up a balloon and stick it in the freezer overnight.


What happened? The balloon will shrink a bit because there is less pressure pressing on the inside of the balloon surface, holding the shape of the balloon. When you decrease temperature, the pressure and volume decrease as well.


Learn more about this scientific principle in Unit 13.



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Click here to go to next lesson on Molar volume of gases and Avogadro’s Law.


Charles Law

Wednesday June 7, 2017

This project is for advanced students.This Stirling Engine project is a very advanced project that requires skill, patience, and troubleshooting persistence in order to work right. Find yourself a seasoned Do-It-Yourself type of adult (someone who loves to fix things or tinker in the garage) before you start working on this project, or you’ll go crazy with nit-picky things that will keep the engine from operating correctly. This makes an excellent project for a weekend.


Developed in 1810s, this engine was widely used because it was quiet and could use almost anything as a heat source. This kind of heat engine squishes and expands air to do mechanical work. There’s a heat source (the candle) that adds energy to your system, and the result is your shaft spins (CD).


This engine converts the expansion and compression of gases into something that moves (the piston) and rotates (the crankshaft). Your car engine uses internal combustion to generate the expansion and compression cycles, whereas this heat engine has an external heat source.


This experiment is great for chemistry students learning about Charles’s Law, which is also known as the Law of Volumes, which describes how gases tend to expand when they are heated and can be mathematically written like this:



where V = volume, and T = temperature. So as temperature increases, volume also increases. In the experiment you’re about to do, you will see how heating the air causes the diaphragm to expand which turns the crank.


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Here’s what you need:


  • three soda cans
  • old inner tube from a bike wheel
  • super glue and instrant dry
  • electrical wire (3- conductor solid wire)
  • 3 old CDs
  • one balloon
  • penny
  • nylon bushing (from hardware store)
  • alcohol burner (you can build one out of soda cans or Sterno canned heat)
  • fishing line (15lb. test or similar)
  • pack of steel wool
  • drill with 1/16″ bit
  • pliers
  • scissors
  • razor
  • wire cutters
  • electrical tape
  • push pin
  • permanent marker
  • Swiss army knife (with can opener option)
  • template

The Stirling heat engine is very different from the engine in your car. When Robert Stirling invented the first Stirling engine in 1816, he thought it would be much more efficient than a gasoline or diesel engine. However, these heat engines are used only where quiet engines are required, such as in submarines or in generators for sailboats.



Download Student Worksheet & Exercises


Here’s how a Stirling engine is different from the internal-combustion engine inside your car. For example, the gases inside a Stirling engine never leave the engine because it’s an external combustion engine. This heat engine does not have exhaust valves as there are no explosions taking place, which is why Stirling engines are quieter. They use heat sources that are outside the engine, which opens up a wide range of possibilities from candles to solar energy to gasoline to the heat from your hand.


There are lots of different styles of Stirling engines. In this project, we’ll learn about the Stirling cycle and see how to build a simple heat engine out of soda cans. The main idea behind the Stirling engine is that a certain volume of gas remains inside the engine and gets heated and cooled, causing the crankshaft to turn. The gases never leave the container (remember – no exhaust valves!), so the gas is constantly changing temperature and pressure to do useful work. When the pressure increases, the temperature also increases. And when the temperature of the gases decreases, the pressure also goes down. (How pressure and temperature are linked together is called the “Ideal Gas Law”.)


Some Stirling engines have two pistons where one is heated by an external heat source like a candle and the other is cooled by external cooling like ice. Other displacer-type Stirling engines has one piston and a displacer. The displacer controls when the gas is heated and cooled.


In order to work, the heat engine needs a temperature difference between the top and bottom of the cylinder. Some Stirling engines are so sensitive that you can simply use the temperature difference between the air around you and the heat from your hand. Our Stirling engine uses temperature difference between the heat from a candle and ice water.


The balloon at the top of the soda can is actually the ‘power piston’ and is sealed to the can. It bulges up as the gas expands. The displacer is the steel wool in the engine which controls the temperature of the air and allows air to move between the heated and cooled sections of the engine.


When the displacer is near the top of the cylinder, most of the gas inside the engine is heated by the heat source and gas expands (the pressure builds inside the engine, forcing the balloon piston up). When the displacer is near the bottom of the cylinder, most of the gas inside the engine cools and contracts. (the pressure decreases and the balloon piston is allowed to contract).


Since the heat engine only makes power during the first part of the cycle, there’s only two ways to increase the power output: you can either increase the temperature of the gas (by using a hotter heat source), or by cooling the gases further by removing more heat (using something colder than ice).


Since the heat source is outside the cylinder, there’s a delay for the engine to respond to an increase or decrease in the heat or cooling source. If you use only water to cool your heat engine and suddenly pop an ice cube in the water, you’ll notice that it takes five to fifteen seconds to increase speed. The reason is because it takes time for the additional heat (or removal of heat by cooling) to make it through the cylinder walls and into the gas inside the engine. So Stirling engines can’t change the power output quickly. This would be a problem when getting on the freeway!


In recent years, scientists have looked to this engine again as a possibility, as gas and oil prices rise, and exhaust and pollutants are a concern for the environment. Since you can use nearly any heat source, it’s easy to pick one that has a low-fume output to power this engine. Scientists and engineers are working on a model that uses a Stirling engine in conjunction with an internal-combustion engine in a hybrid vehicle… maybe we’ll see these on the road someday!


Exercises


  1. What is the primary input of energy for the Stirling engine?
  2. As Pressure increases in a gas, what happens to temperature?
    1. It increases
    2. Nothing
    3. It decreases
    4. It increases, then decreases
  3. What is the primary output of the Stirling engine?

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Click here to go to next lesson on Ideal Gas Law.

Boyle’s Law

Wednesday June 7, 2017

The triple point is where a molecule can be in all three states of matter at the exact same time, all in equilibrium. Imagine having a glass of liquid water happily together with both ice cubes and steam bubbles inside, forever! The ice would never melt, the liquid water would remain the same temperature, and the steam would bubble up. In order to do this, you have to get the pressure and temperature just right, and it’s different for every molecule.


The triple point of mercury happens at -38oF and 0.000000029 psi. For carbon dioxide, it’s 75psi and -70oF. So this isn’t something you can do with a modified bike pump and a refrigerator.


However, the triple point of water is 32oF and 0.089psi. The only place we’ve found this happening naturally (without any lab equipment) is on the surface of Mars.


Because of these numbers, we can get water to boil here on Earth while it stays at room temperature by changing the pressure using everyday materials. (If you have a vacuum pump, you can have the water boil at the freezing point of 32oF.)


Here’s what you need to do:


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Materials:


  • plastic syringe (no needle)
  • room temperature water


Bonus Idea: Do this experiment first with water, then with carbonated water.


Why does that work? How did you get the pressure to decrease? Easy – when you pulled on the plunger and increased the volume inside the syringe. Since your finger covered the hole, no additional air was allowed in when you did this (which is why it was probably a little tough to do), so the number of molecules inside the syringe stayed the same, but the space they had to wiggle around got a lot bigger, meaning that the pressure decreased.


The air inside the syringe isn’t just plain old air… it has water vapor inside, too. And that’s not all – the water from your sink isn’t just plain old water, it has air bubbles mixed in with it. When you brought down the pressure (by pulling the plunger), you are forcing the air bubbles to come out of the water, which makes it boil. When you shove the plunger back in and increase the pressure, you’ll find that the air bubbles mix back into the water and disappears.


Did you try the soda water yet? Soda has carbon dioxide already mixed in for you, which is under pressure. You can release this pressure by opening the bottle (you’ll hear a PSSST!), which is the carbon dioxide bubbles coming out of the soda. Go ahead and try that now before reading further…


When you place the soda water into the syringe and decrease the pressure, the carbon dioxide comes out quickly Try tapping the syringe to make all the tiny bubbles combine into one larger bubble. When you increase the pressure (push the plunger back in), some of the bubbles will redissolve back into the soda.


If you’ve ever had a glass of hot water suddenly erupt in an explosion of bubbles, you’ve experienced superheated water (water that’s above it’s normal boiling point) that hasn’t been able to form bubbles yet. By adding a tea bag or simply just jiggling it around is usually enough to cause the bubbles to start, which often splatters HOT HOT water everywhere. (This isn’t something you want to try without adult help.)


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Click here to go to next lesson on Charles Law.

Gases

Wednesday June 7, 2017

Here are the most important things about gases to remember:


  • Gases assume the shape and volume of their container.
  • Gases have lower densities than their solid or liquid phases.
  • Gases are more easily compressed than their solid or liquid phases.
  • Gases will mix completely and evenly when confined to the same volume.
  • All elements in Group VIII are gases. These gases are known as the noble gases.
  • Elements that are gases at room temperature and normal pressure are all nonmetals.

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How do they make liquid helium, liquid oxygen, liquid nitrogen… atoms that are normally in the gases state?


The basic idea is that they compress the gas (remember the room full of ping pong balls? Now squish the room so it’s only half the size. Do the balls bounce faster or slower? Faster! So the temp increases.) When they compress the gas, it heats it up, so they cool it, then squish it even more to higher pressure and cool to near room temperature. They keep repeating this until it becomes a very high pressure, then finally they release the pressure (which is like suddenly expanding the squished room to the size of a football field), which makes the temperature drop way fast and the gas becomes extremely cold, condensing into a liquid.


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Click here to go to next lesson on Boyle’s Law.